i think he said it was unlocked when he bought it.
the act of unlocking wouldn't create those problems. it does sound like the sims card or sim card dock is faulty or loose. i'd go to cingular and tell them that you lost your sim card. your allow 2 sim card activations a year,free of charge. that will at least, eliminate the possibillities of it being the card.and if you don't already have one, they give you a 64K card

then i'd try checking the dock for it being loose or dirty.
if it still dosen't work. it's the software on the phone. get with me if you get to that point