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I update my iPhone 4 last night and iMessage did not install. I used the Search iPhone for it too without success.
 
I'm having this problem too. My iPhone seems to work fine. When texting a known iOS5 device, it says "iMessage" in the text line and the text balloons are blue.

I just update my wife's iPhone, and she can iMessage my phone; but I can't iMessage her (it defaults to green text message from my phone). Basically her phone number is not recognized as belonging to an iPhone. I can iMessage her, however, when I text to her Apple ID.

Any suggestions would be appreciated! Am hoping it has something to do with AT&T lag and slow servers today.
 
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