Not sure if anyone else has had this problem, but it looks like yesterday’s iOS 5.1 update turned off iMessage support, at least on my AT&T iPhone 4. A quick trip to Settings→Messages→iMessage was all that it took to get iMessages working again (they had somehow been turned off during the update).
Anyway, just posting in case someone else is trying to figure out why their iPhone suddenly stopped receiving iMessages.
Happens to me to
The same problem in Europe. iMessage is not working ( I cannot send an iMessage) with iOS 5.1 on iPhone 4S even after full re-installation of the software.
same thing happed to me – was working fine last night, but after all i devices were updated – my ipod can no longer receive imessages from husbands iphone. i have tried everything including the magic dns 8.8.8.8, but nothing is working.
after 5 tries of activating and deactivating – it is working again, for the moment.
I didn’t update the firmware yet. But this shit happened to me too though!!!!
这个问题也同样发生在我身上，我试尽各种办法（reinstall, UDF mode, switched off…..）怎么都没用。实在不明白到底发生了什么。
My message was not working. I fixed it by changing dns settings on my device. I followed these tips
http://appletoolbox.com/2011/10/ios-5-imessage-not-working-–-how-to-fix/
Disabled iMessage on my ios 5.1, the same problem I saw on iPhone 4 also, and I want to enable it how to enable iMessage on iPhone ios 5.1.