Getting another user's iMessages

It's definately not associated with my iCloud account anymore, which is separate from iMessage, so no go on the remote wipe.

I do appreciate the help, but with this thread I am most interested in finding out if anyone else has had this problem. If it is not a fluke, then putting someone else's SIM in your phone temporarily (long enough to make your phone think it has that number), could gain you access to said person's sent and received iMessages indefinately, which is pretty concerning. Since my ticket is being escalated to engineering, I am more inclined to leave the situation as it is for now, so that they can diagnose and patch it, if it's a legitimate issue. I honestly can't see how it's not a real issue, though, even if a factory reset worked.

I think the solution in this case is to require a SIM when sending & receiving iMessages against your phone number (as opposed to your Apple ID, which does get cleared with the erase.) Otherwise it seems like there is a lot of potential for abusing one's privacy, especially with the jailbreak / hacker community.

Right, and I kept my SIM. I was suggesting that, since iMessage identifies you with either (or both) your Apple ID or your number, it should require the SIM for that number to be present in the device when sending / receiving as that number. When you activate iMessage under your phone number, AFAIK you are not asked for any other credentials, so activating / using a number that you no longer have the SIM for should not be allowed. It appears to be allowed, in my case.

Update: If you sell your iPhone, remove the SIM BEFORE you erase or restore factory settings on the device. I can reproduce this using my iPhone 3GS, and I can confirm that it indeed is an issue. If you restore iOS or erase all contents and settings, and your SIM card is in the device when it is activated (as you would need to do to demonstrate that the device is still working) it will by default enable iMessage under your phone number, which will continue to work long after your SIM is removed and after the phone is in someone else's posession. This happens even without entering your Apple ID (during setup or otherwise), without making any calls with your SIM in the phone, without sending any text messages with your SIM in the phone, and it happens by default!

My ticket was escalated to engineering and they informed me that it was a known issue that they were investigating. They also said they had no way to stop this person from receiving my messages, and sending messages as me. Since it is using my phone number and not my Apple ID, there are no passwords to change or anything that I can do aside from hunting this person down. My only hope is that this person will eventually respond to my messages, but so far no luck. I know my messages are still being sent to this person, because I can turn off iMessage on my new phone and iMessages still go through to "me" from my wife's phone. I am also receiving messages sent to, and from this person.

In addition to this, fairly common scenario (I found countless threads on other sites about this, since posting), I can imagine someone exploiting this by:

1. Taking a spare iPhone with iOS 5 installed (e.g. an old 3GS) and do an 'erase all contents and settings' (only takes a few minutes)
2. Borrow or otherwise get posession of someone's iPhone and activate your newly wiped iPhone with their SIM (again, it only takes a minute to do)
3. Restart the device (not sure if this is nessesary)
4. Replace the SIM into the original device, and return and/or replace the iPhone you "borrowed". You will now receive all of that person's sent and received iMessages (as long as you are on WiFi), and even Apple (apparently) can do nothing to stop it. If you never send any messages, they may never find out you are reading their messages! Even if the person turns iMessage off on their device, iMessages sent to this number will still be successfully sent... to you! The only way to stop it is to have all of your contacts disable iMessage as well.

Here's hoping for a fix, really soon...

I highly recommend you contact iPhone support and get it escalated to engineering (1-800-MY-IPHONE). Supposedly they cannot turn the other device off, but they say they are working on it, and in my case could tell me at what date the iMessage activation on that device expires (I think it was a little over 6 weeks in my case.)

After that, to test if the other guy was still getting my messages I would periodically turn off iMessage on my phone, then send myself a message from another iPhone. If the message is marked as "Received", then someone else is still gettting it. For two days I bombarded this person with strongly worded messages telling them to turn off iMessage (I believe it verifies once you turn it back on, so I am hoping he cannot turn it back on), erase & restore, or install a SIM. They never responded, but iMessages are no longer going through when iMessage is off on my device. I must have annoyed them into submission...

Other things you can do: change your 'Caller ID' in your message settings to your Apple ID. That way when people respond to your iMessages, it won't go to this person (who is only receiving messages sent to your #). I'm assuming your outgoing messages are not seen by this person when you send as your 'Apple ID', but I'm not 100% sure. -- Don't do this if you are trying to message this person, though, as they will not get them. Also, make sure when you 'test' to see if this guy is still getting your messages, that you are not sending messages to your AppleID from the other phone, but to your number...