Unless they changed it recently It should work with a balance to telus as I know someone who did it a few months ago. No u don't have to unlock it. But I reccommend paying telus off first. So u don't get too far behind.
One you port over to Tellus, Tellus will charge you the amount owing for your phone. There is no way around it. I would contact Tellus and find out from them what are the costs when you cancel and then decide what you want to do.