Quick iPhone registering question

I sold my original iPhone to friend who went and activated it to their number.

However, when they try and download an app from the store it my itunes account pops up and asks them for my information for iTunes log in...

How do I fix this?

 

Is there anyway I can fix this?

The phone was used by myself and before I sent them the phone i upgraded to version 2.0 and chose to restore the phone from the "settings>general" tabs.. the phone took about 45 minutes to clear the data.

They did activate the phone to their number through iTunes, however When they used the app store a message popped up asking for MY iTunes login information, not theres..

Can anyone be of any assistance?