V300 Help switching from T-mobile to Dobson/Cell One

Hi.

It doesn't look like this forum gets a whole lot of traffic, but if anyone could help me, that would be great.

I have a unlocked V300 phone that I bought. It was made for T-mobile. I need to switch the carrier to Dobson/Cellular One. I put in the sim card, and it doesn't work. For instance, I'm only either in extended area, or I have no signal. When I can make a call, I can't hear anything through the headset.

I was told that T-mobile phones used a different frequency than Dobson/Cellular One, but I was also told that it would still be possible to make the switch. Is there anything I can do, or am I just SOL?