can any other cell phone from any other carrier like rogers telus fido be

used on my bell plan? so i just recently updated my phone to the LG xenon and i hate it already. i signed a 3 year deal with them and since its new bell just came out with sim cards so i do have a sim card. can i use a phone from any carrier listed above and use it? do i have to unlock it or what? thanks in advance. ps im canadian