Would previously sent iMessages old messages show up on another iphone if same phone number used

recently, I used my uncles iphone 4 to imessage my friends. my uncle recently decided to give it to me and get himself the new iphone 4s. Since its from out of country, we went to unlock the iphone 4 and got rid of the old sim card and he got a new sim card with the old phone number (same number for iphone 4).

my problem is that im scared he'll be able to receive my old and new imessages. I had deleted them on his old iphone and reset the whole thing twice.

the problem is that on the old iphone, I did input my own apple ID to send messages, but I realized later on that it was using the PHONE NUMBER as the CALLER ID. Sure the messages still synced into my iPod 4g and back and forth.

I heard that sometimes, two iphones that had the same sim card or phone number tend to send to each other messages as if it was one phone and that concerns me.

Is it possible that when he activates his new iPhone, the old imessages would show up on his phone as syncing? I really don't want him to get his hands on my old messages.

I heard that sometimes, two iphones that had the same sim card or phone number tend to send to each other messages as if it was one phone and that concerns me.

thanks.

btw both phones have the new iOS 5.1.1