Sign a 3 year contract or buy the phone outright?

Hey guys I'm just wondering if someone can give me some helpful advice as I've been battling with these 2 ideas for awhile now. I wanna get the new HTC Sensation from Bell and its probably around 550 to 600 dollars outright. Or there's a 3 year contract option where i would prob pay 50-100 dollars or so for the phone. I'm a full time University student with a part time job so I'm a little worried about signing for 3 years in case I cant afford it or I have to quit work etc during the duration of the contract (min plan is 50 dollars for a smartphone). I wanna make the right choice obviously so does anyone know what the cancellation fee of the contract is i hear it was 400 dollars plus a data cancellation charge? What is the data cancellation charge and what do you think the best option is? Any advice would be helpful.