Buying a used cell phone

I have a few questions regarding buying a used cell phone. Right now my boss pays 100% of my cell phone bill. I am laid off but he is still paying it. When he laid me off he had AT&T turn off my data package.

My Blackberry is almost toast and I need to get a new phone. If I upgrade through AT&T I will get roped into having data which I don't need right now and chances are he will make me pay for my phone again.

My questions are:

Will any blackberry work if I use my sim card in it? Does it need to be an AT&T phone. If I did buy a used phone would I have to get a data package?

All I want is my phone to work and I am partial to the blackberry.

Thanks for any help.