Can I buy a phone off ebay and use it with my already established(bell canada) plan??

Stupid cell phone isn't working well and I'd rather upgrade than have all the shenanigans bell wants me to go through... and they won't let me. They're "loaning" (RENTING) me a phone, while their pos phone gets fixed... So, can I but a bell phone and register my plan to it? How does this work??