It depends on the phone really. If, for example, you pick up one of the original Google Nexxus phones then as long as it's radio band is the same as Bell's then you can just pull the SIM from your I7500 and slip it into the Nexxus. You don't have to deal with Bell at all.
FWIW I just dumped my I7500 (giving it to my son after less than a year) and re-contracted for the Desire Z. It's a totally different experience than running Galaxo or GAOSP on the I7500. I thought about the Galaxy S but I don't trust Samsung anymore as far as phones go.