My iMessage is doing something interesting... First of all, no sim cards were exchanged between devices that I have problems with.
Here is the situation, I have 3 iPhones under my apple id* iPhone 4s, iPhone 4, iPhone 3Gs. iPhone 4s and iPhone 4 are on AT&T and iPhone 3GS is under international sim card(unlocked) All 3 phones are on iOS 5.0.1 and iMessage activated under my apple ID. For the first month everything worked well, imessages got where they were supposed to... Untill I upgraded my iPad 2 to iOS 5.0.1 and activated imessege there. I sent message from iPad 2 to a phone number on iPhone 4 and the message went through... I replyed from iPhone 4 to iPad 2 and message also went through(with delay!). Later I found out that on iPhone 3GS the whole conversation between iPhone 4 and iPad 2 appeared... As if it was sent from iPhone 3GS. I agree, that because everything is under one apple ID this is expected to happen(I still think that is wrong!)
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So to make things easier I removed iMessage from iPad and removed all of the conversations that were made between the devices. I also restarted iMessage on all the phones.
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Now this is where it's getting interesting... It doesn't always happen but happens often enough! When iMessage is sent from iPhone 3GS to iPhone 4s they appear on iPhone 4 as if they were sent from iPhone 4 and when I reply to iPhone 3GS they appear as a reply on iPhone 4(it's driving me crazy...) When message is sent from iPhone 4s to iPhone 4 they appear on iPhone 3GS as if they were sent from iPhone 3GS... Now, I also figured out that the messages that are being miss delivered are messages that were not sent initially because of network problem. If iMessage that I'm trying to send gets (!) it will be miss delivered to another device. I don't know if this is a problem in my situation... It's also hard to explain so I'm doing my best...* I would like to know if there is a fix for that in the works? I'm changing the email addresses on devices and will see if that helps. If you have something that sounds similar please share...
Yes, this happens when a contact in the address book has a phone number and an email address attached to iMessage service on a different phone (in Settings, Messages, Reveive At), on the iMessage server that phone number is attached to UDID of one phone and the email address is attached to UDID of another phone or idevice.