Can anyone tell me if an LG CU500 can be used on Cellular One?

I have tried 2 of them now, purchased from eBay. Both were Cingular phones advertised to be "unlocked". The 1st one, a new phone, just came up with "Network unavailable" when I tried to make a call. The SIM card was from a RAZR I was using on Cellular One. The 2nd one, a used phone, with the same SIM card, actually displaed "Cellular One" on the screen after I enabled wireless on it, but it also displayed "Network unavailable" when I tried to place a call. The screen also no longer displayed "Cellular One". Now the SIM card doesn't even work in the RAZR. It does not display any signal strength bars or "Cellular One" when I power it on and it goes through a "searching for network", "registering" sequence. It does not display any error message until I try to place a call and I get "Call failed".

I don't know where to go from here except to maybe try an unlock service because maybe these phones weren't truly unlocked to all carriers?

Any help would be appreciated.

jekes