How to remove my phone number from my old deactivated iphone?

I just upgraded to the new iphone and completely restored my old iphone 4 so my sister could use it as an acting itouch but when you go to the imessage settings my number is still there.
how do i remove my number from it so that it's just her email?

Hi
i just came here for the points
bye

Try taking it to an Apple store? Only thing I can thing of since you already restored