iPhone How often does iMessage check in with the carrier?

[soy]

I recently moved from the UK to the US and cancelled my UK mobile contract. The contract got shut off the other day, with the iPhone saying "No Service" in the status bar and basically being a glorified iPod Touch.

As far as I understand (but correct me if I'm wrong), when activating iMessage the phone sends a hidden text or data message to the carrier and receives one back (all hidden from view) to confirm the phone number.

I'd imagine that after initial activation it does this periodically just to confirm the number is still the same (I know that in the US deactivated numbers get back in circulation relatively quickly, so Apple and the carriers have to somehow make sure that you don't get the messages of the new owner of the number, in the UK it takes quite a while for a number to go back on the pile of usable ones).

I won't be able to get a new T-Mo US sim for at least a week or two, so I'd like to still be able to use iMessage on my old number. At the moment this still works without problems.

How long will I be able to keep iMessage working on my old number before it checks the number with the carrier and realizes it doesn't exist anymore?



TL;DR: My number is no longer in use, how long can I keep using iMessage on it?

 

[Gav2k]

I might be wrong but it takes the information from the SIM card. No hidden messages are involved.

 

[leventozler]

Sends it once to Apple to activate iMessage/FaceTime. You should be able to use it with same SIM card. I'm not sure if someone else activates your old number and tries to activate iMessage...

 

[bbrks]

iMessage works with both, your number and E-mail address. If your UK number is already deactivated, than you still have iMessage only with your E-mail.

 

[gordon1234]

I might be wrong but it takes the information from the SIM card. No hidden messages are involved.

Actually he's right. At least for most carriers, iMessage sends an SMS to confirm your number before activating. This is done silently in the background so you never actually see the message. Whenever I pop a new SIM card in when traveling, I'll get a message stating that iMessage needs to send me an SMS to complete activation and that charges may apply. I assume this is to confirm the phone number is truly assigned to your device. Apple's servers message it, then the local iOS confirms to Apple that your device received the message.

 

[Gav2k]

I'm thinking that's the two step authentication more than iMessage assigning the number as that information can be pulled from the sim. Hence the need for a data connection

 

[xero9]

In my experience, you can use it indefinitely. Once activated, it should continue to work. My father had a cancelled SIM when he moved from iPhone to Android and it continued to work on his iPhone for over a month until he finally de-activated it.

The only way it would stop working is if you use the de-registration option Apple provided not too long ago, if you turn off iMessage on your phone, if you switch your SIM, or possible if they hand out your number to another iPhone user (though it's unlikely they'd give away your number so quickly).

In any case, you can keep using it for at least two weeks when you get T-Mobile in the US.

 

[soy]

Looks like it'll be fine then, thanks everyone!

 

[bertbekkelik]

I might be wrong but it takes the information from the SIM card. No hidden messages are involved.

Your iPhone does send a text message. I don't know for US citizens but for Europeans, the text message is being send to the UK (or maybe they just don't have one for Belgium, and our phones send a text to the UK too, I don't know).
On my previous service provider I got this 'apple one time activation' thing which actually was a text to the UK but my provider didn't charge me for it.
I'm on another provider now, and this one just bills it as a normal text to the UK (so I have to pay extra, because I'm texting a foreign number).

Your iPhone sends a text to apples servers with information in it. The servers know what number the text is coming from and they know what iPhone it's coming from by the information in the text. Your iPhone gets activated and iMessage works over your phone number.
iMessage would work without this, but only via email.

I went over my plan this month, and I set a cap that I could only go over it for €5. I did so now I can't do anything except using my data bundle. Someone sent me a really important message via iMessage and someone else tried to FaceTime me but I didn't receive anything, and apparently, my phone was trying to activate iMessage and FaceTime. So yes, I think the iPhone does periodically check if your phone number is still the same.

And if one iPhone activates a new phone number, it'll be deleted from the one that had this number activated before. In fact, I even have to reactivate iMessage everytime I've put another SIM card in my phone for 5 seconds.