I just bought a Blackberry online and now i need a line for it.

We have a family line with T-Mobile which i could get included in, but i really don't want to extend the contract.

I also don't want to pay $50+ just for my line by starting with a new network.

What is the best deal for Blackberry's?

P.S. - As far as i understand, you can use it as a standard phone with a regular line, but I would like internet (preferably unlimited) aswell.