my father just got the new 3gs, after his contract for the iphone 2g was done, and he gave his old iphone 2g to me. when we got it, att gave me a new sim card for me to use with the iphone. i put in my old sim card, which was from cingular, into the iphone 2g. my trouble is, sometimes it's slow and has bad reception. could that be linked to an old sim card? should i put the new one in? and if so, how would i do that? thanks.