3Gs issue just started

Recently upgraded to IPhone4 and wife beneffited by getting my 3Gs which i got on day of release last year.
Since wife started using (i did factory reset and set up for her) it seems to freeze and lose calls. While she is talking on phone, it cuts the call off and shows the apple logo for about 1 minute or so before recoverring.
Is this a simple case of try factory reset again or could it be something more?
Thanks for any help
Wayne

 

Re:

I was looking for advice on which of these would most likely work really. I don't get why it seems to shut itself down or freeze, or whatever its doing.