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Posted on November 3rd, 2011 by Barry Collins

How iMessage works

iMessage iPad

One of the best new features in iOS 5 is iMessage. This nifty little service subverts the traditional SMS text messaging system, allowing you to send free* text/picture messages to other iOS 5 users via the data channel (*free, presuming you don’t exceed your data cap, that is).

iMessage is very subtly implemented into the existing Messages app. You won’t even notice it until you attempt to send a text message to a contact with an iPhone, and the message suddenly goes blue. Apple automatically detects when the recipient is using iOS 5 and diverts the message via the data channel rather than your network’s SMS channel.

iMessage iPhoneAs PC Pro’s Paul Ockenden has argued repeatedly in his Real World Computing column, SMS messages are only a few bytes of data anyway, and it’s amazing that the mobile networks have got away with charging separately for them for so long. However, if you’re on a monthly contract, chances are you’ll have several hundred – or even thousands – of inclusive SMS messages anyway, so the cost benefit of iMessage is likely to be slim.

Perhaps the biggest benefit of iMessage is that it allows you to send text messages even when you’ve got no mobile reception. In my house, for example, there are rooms where I can’t get a reliable phone signal, but the iPhone is constantly connected to the Wi-Fi network, so I can send and receive messages (admittedly, only to/from other iPhone users) without having to dangle near an upstairs window. Alternatively, if you’re abroad, you can hook up to the free hotel lobby Wi-Fi and exchange text messages without paying extortionate roaming text tariffs.

Back to SMS

What happens, you may wonder, if the inverse is true: you’ve got mobile reception but no data, such as when you’re abroad and out of Wi-Fi range, and have turned data roaming off to avoid horrendous roaming charges. Do messages sent from iPhone contacts not get through, because there’s no data channel available?

The answer is no. If you send a message to a fellow iMessage user who has their data switched off, the phone attempts to send it via the data channel at first, but if it can’t get through after five minutes or so, the message turns green and is sent via the traditional SMS channel instead.

This could mean that you’re charged for sending an SMS message that you thought you were sending for “free” via iMessage – there’s no prompt to ask whether you want to send via SMS, it just does it automatically – but the amounts involved here are so tiny that we don’t think it’s a serious problem.

The other small advantage of sending texts via iMessage is you get an instant messaging-style speech bubble on the screen when the other person is typing a message to you, so you know when you’re about to get an incoming message.

iMessage bubble

iPad messaging

iMessage also works on the iPad, allowing you to send text messages even from devices without a 3G SIM. Synchronisation is a little patchy in our experience with a Wi-Fi only iPad using the same iTunes account as an iPhone 4S.

Messages sent from the iPad are synchronised to the phone, but not the other way round, unless you’re replying to the same thread. So you can start a conversation on the iPad and pick up where you left off on the phone, but not necessarily the other way round.

Full iMessage synchronisation between iPad and iPhone is apparently possible between 3G versions of the tablet, but we haven’t been able to test that.

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37 Responses to “ How iMessage works ”

  1. Ben Says:
    November 3rd, 2011 at 4:20 pm

    How does it know your contact has an iPhone? Does an SMS have some kind of tag on it to say what phone a person is using?

  2. Ben Says:
    November 3rd, 2011 at 4:21 pm

    or does it check numbers against a central repository held at Apple?

  3. Scottbag Says:
    November 3rd, 2011 at 4:42 pm

    Nice. Is this possible on Android? I know whatsapp messenger is available but this isn’t integrated with the sms functionality as far as i can tell.

  4. Stu H Says:
    November 4th, 2011 at 10:25 am

    OMG, this is such a ’slavish’ copy of MSN IM, et al,

    Let the lawyers fees role lol

    But please PC PRO, why is this worthy of a blog post? Blackberry have seen doing phone IM since who knows when and SMS/IM flip is hardly ‘magical’ even by apples stretch of markating!

    Fan boys ;-)

  5. Jim Says:
    November 4th, 2011 at 10:42 am

    Am I the only one that doesnt get this?

    Often yo get thousands of txt messages for free and if you go over your allowance they are only 12p or so anyway. Data on the other hand has a very low limit and if you go over is hideously expensive.

    Not only that but why? It only works iPhone to iPhne anyway. Sure if you have no signal but wifi it’s OK but why not get a SureSignal or similar and get perfect reception to txt message anyone?

    This is another step backwards, away from an open standard that works perfectly but the Apple fans seem to think it’s a great idea.

  6. David Wright Says:
    November 4th, 2011 at 10:57 am

    @Jim you are looking at it from a European / World perspective. In America, you have to pay to receive SMS as well as send them!

    If you haven’t taken out a flat-rate option, that could become expensive.

  7. Austin Says:
    November 4th, 2011 at 11:41 am

    Meh… another crApple *so what?*

  8. Andrew Harvey Says:
    November 4th, 2011 at 12:31 pm

    WhatsApp Messenger seems great to me. Use it from my phone via 3G or WiFi to send messages to family abroad – no extra cost – unlike SMS.

  9. Jon Says:
    November 4th, 2011 at 1:23 pm

    In the U.K we may get contracts that include a large number of free SMS/MMS message but I believe in the US that this is not the case. Each message is charged for so over the pond it’s going to be a big thing.

  10. Chriz Says:
    November 4th, 2011 at 5:05 pm

    When sending a text message, it is over the signalling network. When sending a picture message, it is encrypted (GPRS). Storage of messages will be governed by the operator which is under tight regulation.
    What protects the user when using this method? Messages sent using TCP/IP which can easily be intercepted, and possibly/probably stored in a simple file format on a load of servers in Apple land …hackable??? ..look at the problems with Sony…
    I haven’t read any statements from Apple on their security or regulation, or even read the terms, so perhaps my comments are not warranted. It would be useful for a reporter to invetigate and comment on these issues.

  11. dave Says:
    November 6th, 2011 at 9:05 pm

    Brilliant another first from Apple.

    Well not quite, have a look at Viber or PingChat, they’ve been doing exactly this for quite some time & they’re cross-platform too.

  12. Ossie Says:
    November 7th, 2011 at 8:35 am

    Have been wondering how my iphone 3 gs ios 5 had been receiving message with no sim card. now I know. Thanks

  13. John McLean Says:
    November 7th, 2011 at 3:14 pm

    You say “there’s no prompt to ask whether you want to send via SMS, it just does it automatically”.

    You can change the settings so it doesn’t automatically switch to SMS. That way you get a little red exclamation mark to show message failure, and you can choose “try again” (via iMessage) or “send as SMS”.

  14. John McLean Says:
    November 7th, 2011 at 3:22 pm

    @Jim – yours seems to be a common misconception, and is one which should be put to rest. iPhone contracts typically come with 1GB+ of data per month, which is massively more than enough for all the iMessaging you could possibly want to do. The costly things on mobile data are watching video, video calling, and downloading music, videos and apps. Short ASCII messages use negligible data. 160 characters plus a generous allowance for headers and you’re still under a quarter of a kB, so you could do 4,000 for 1MB or 4,000,000 for 1GB – doesn’t look so bad now, does it?!

    Okay I agree re bundled texts, but 12p per message out of bundle is outrageous for the amount of data in qusetion. Even at extortionate £5/MB roaming rates you could send dozens of messages for 12p.

    Also what about international messages? I have friends abroad, and sending SMS to them is expensive and not included in bundled texts. Or when roaming – I’d rather pay a few pounds in roaming charges for a lot of messaging rather than 40p+ per message for roaming text charges.

    Also picture messages aren’t cheap and usually aren’t included in bundles, whereas with iMessage it is just the data usage.

    Finally the ability to send over wifi is great for areas with poor mobile reception. It doesn’t supplant messages over mobile data / SMS, but surely having more connection methods and switching seamlessly between them is a good thing?

  15. SM Says:
    November 8th, 2011 at 4:09 am

    The coolest thing about this is “texting” using the recipient’s .me address instead of a phone number. I’m in the US and just chatted with an expat friend in SE Asia using iMessage between my WiFi-only iPad and his iPhone4. To both of us it looked like any other text message. Sent pics, vids, and plenty of text. Excellent and free.

  16. MGV Says:
    November 8th, 2011 at 9:33 am

    I find iMessage useful as like Barry the mobile signal at home is very poor. I can now send messages using my i Pad 1(no 3G) at home using wi fi. I can send messages to my grandson on his i Pod Touch using his hotmail address. He does not have a mobile phone but will need to teach me how to talk in “text” language!

  17. nila Says:
    November 8th, 2011 at 9:54 am

    Find this article really lacking to be honest.
    No mention of the hugely obvious and important “allows you to send free international messages which are extortionately priced” and I presume it does the same for sending pics etc.
    Also, at one point in the article you mention how it can save you money when roaming, then go on to say how it will automatically switch from iMessage to an SMS and dont point out the hugely obvious that if you are roaming this is suddenly going to end up costing you a fortune.
    Also, when you are roaming or want to send to someone abroad, there is no way to tell that you can send it to them for free until you try to send the message and so it really doesn’t help you easily see which of your friends abroad you can communicate with for free.

    WhatsApp is definitely a far better solution, especially for the fact it works across BB, iPhone AND Android phones.

  18. Stu H Says:
    November 8th, 2011 at 12:15 pm

    @SM & MGV

    I doubt anyone will argue it’s a nice usefull system, but as pointed out above it’s neither new, magical, and barely news worth apart from it’s Apple!! You could do all of this already with 3rd party solutions, cross platform!

    I would love to know if apple have applied for patents for this wonderous ‘new’ function ;-)

  19. Paul Anderson Says:
    November 9th, 2011 at 1:05 pm

    My partner and I each have an iphone 4. We only have one laptop we use to sync to itunes. We can’t have two itunes accounts on one pc.

    We got the iOS 5 update with imessage, and then realised that as you can only have one itunes account per laptop, and therefore one imessage account, we started receiving each others text messages from friends also using imessage. The only solution I know of is to either buy another laptop/PC and set up a seperate itunes account, or switch off imessage.

    We have switched off imessage.

    Thanks Apple … one button on the hardware …. no understanding of how it’s users use the software.

  20. dave Says:
    November 9th, 2011 at 6:46 pm

    Paul – separate user accounts on the laptop should sort that out.

  21. Phil Sayer Says:
    November 10th, 2011 at 7:00 am

    A big drawback (especially as you can’t control it) is the delay between the phone realising the recipient isn’t connected to the internet, and sending it via SMS. We’re used to texts working almost instantly, but there can be a five minute lag now.

    iMessage is little more than Whats App, re-badged and taken in-house, but in doing so Apple has hobbled a key service, namely SMS/MMS.

  22. Paul C Says:
    November 10th, 2011 at 7:29 am

    @Paul Anderson Offers a solution if you gave another mail address to use but doesn’t need another AppleID

  23. Anthony G Says:
    November 10th, 2011 at 8:46 am

    In addition to the obvious international benefits, in HK you are charged for SMS between the mobile networks, so solutions like these are very useful. iPhones are extremely popular here so it will be interesting to see how competitors last.

    Just another snippet for the uk-centrics…

  24. Peets Says:
    November 15th, 2011 at 11:19 am

    I’m astonished that NO users seem to care that they are in principle contributing to a global tap on SMS messaging. SMS messaging remains normally “in country” between users. Apps like WhatsApp as well as iMessage export this information to the US. Fantastic that people are not bothered anymore – what a few years of brainwashing can accomplish is amazing..

  25. Tim Says:
    November 21st, 2011 at 8:28 pm

    @Paul Anderson
    you can assign a different imessage-adress (has to be an apple-id) to the devices under settings-messaging… theyre just plain apple-ids, no need to sync via itunes, etc.

  26. bimmer Says:
    November 22nd, 2011 at 9:59 pm

    Hats off to Apple for finding another way to screw the carriers. Here in Canada the SMS rates are 15 cents each way. I am slowly turning into a fanboi.

  27. rammblings101 Says:
    December 3rd, 2011 at 10:35 am

    So the system is supposed to know when the recipient can’t receive iMessages and sends them by SMS after 5 minutes? Not for me it doesn’t. Only found out after 12 hours that none of my last 8 iMessages have been received. Switched off iMessaging now! Sorry Apple but technology not good enough.

  28. szecs Says:
    December 3rd, 2011 at 12:20 pm

    Can I send iMessage from PC to iPhone? I have not got iPhone.

  29. Alex Says:
    December 5th, 2011 at 12:40 am

    As an American user I am very happy: txt messages to any other country is 25c a message – and biggest plan is 100 messages a month. After that it’s 1 buck for every message – in and out. Adds up fast when your family and friend are all overseas. This is saving me about a 100 bucks a month. Excellent. Does it also work an iPod?

  30. James Says:
    December 6th, 2011 at 4:26 am

    You can switch off the “auto send as SMS feature” in the settings menu.

  31. Cece Says:
    December 6th, 2011 at 1:23 pm

    If I swith off the “auto send as SMS feature”. Can the message been send anyway if the receiver has dataroaming off. Do you get manually a choice for “sms” or “imessage” ?

  32. Alan Says:
    December 19th, 2011 at 6:59 am

    iMessage also works on iPod touch, which adds more value to the device.

  33. Alicia Says:
    December 29th, 2011 at 11:19 pm

    My iPhone is not getting messages, but my iPad is getting them…..both with same settings. What gives??

  34. lee Says:
    January 31st, 2012 at 10:27 am

    I initially had a little trouble setting up imessage between our WiFi only iPad and my iPhone with the same Apple ID. I got around this by assigning a separate email address to the iPad and voi la, it works beautifully. If you check the message settings, under ‘receive at’ setting you can add another email address.

  35. Rodney Says:
    March 12th, 2012 at 6:48 am

    Okay. So I’ve set up my iMessage information for sending/receiving SMS. I do not have a sims card however. I’ve been reading that you can text without the need of a sims card. Is it only to other iDevices? I cannot seem to get it to work. It just keeps telling me no sims card installed every time I try to send a message. Currently an upgraded 3GS (5.0.1).

  36. Rodney Says:
    March 12th, 2012 at 6:49 am

    By the way, I am on a WiFi connection.

  37. Amanda Says:
    December 25th, 2013 at 5:14 pm

    I just got the IPhone 5c! I was texting my friend on iMessage but than turned my data off so it went to normal text messaging when it was on normal text messaging I texted something else to my friend and got no reply. I didn’t think anything of it until I turned my data on about 20 minutes later and it came up on my texts I had received a text from her 18 minutes ago! So my question is can I only receive other iMessages when on iMessage?


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