.....have active cell service with a provider? If so, which one? Have you ever had cell reception on that phone? Where are you?
You haven't provided enough information for anyone to offer advice.
I have a Galaxy S, unlocked from AT&T, aka samsung captivate.
It recently stopped getting service. I think it realises that there is a SIM, it just won't get reception. I tried with a few netwroks, in two countries, nothing doing.
Wifi wroks, bluetooth works... just cell reception missing. Now it's like I've got a Samsung version of the iPod Touch
As you may have guessed, it's out of warranty, though in great condition.