razr compatible with existing service?

I recently purchased a brand new motorola razr still in the box from ebay. It said that its compatible with t-mobile service. I have my existing service with cellular one and I simply thought that i could just use my sim card that i already have for the razr phone. After thinking about it, the phone would most likely be locked since its brand new. Would i be able to take the razr to cellular one and get it unlocked there or could i just use the sim card i already have? I have not received the phone yet, but should get it in a couple of days.

Cellular One will not unlock your phone, you will need to get it unlocked as you already know before you can use your sim card.

Thats what i thought. So how would I get my phone unlocked then? There is no tmobile service anywhere near my area. Ive heard about getting them unlocked on the internet. Does that actually work and whats a good site for that?

Yes you can used a remote unlock service, just google it and it will bring up plenty of sites, you can also try an independent cell phone shop, they will usually unlock phones for about $20....good luck.