My Iphone 3gs was stolen. I got a new sim card and kept my same number, however, when anyone from an Iphone tries to text message me, it turns it into an imessage and goes to my stolen phone so the person with the stolen phone is getting all of my message
My wife was having the problem that texts to her were going to both of our phones, and texts from her were showing up to her friends as coming from me (even though she was sending them on her phone).
Your suggestion ("Settings>Messages>Receive At...you need to remove the email address you have listed here") appears to have fixed this problem. On her phone, we turned off iMessage, turned it back on, and removed my email address from there. Now it appears to be working correctly.
Don't know why after several months of us both being on iOS5 this suddenly started happening the other day, but at least your fix worked. Thanks!