Basic buying consideration:
1. Coverage: Every service provider have their own coving zone, so make down where you are mostly involving in the phone call, to compare their coverage. And also, do you plan to travel quiet often? Does the destination you are going to go have the service agreement with the service provider here?
2. Plan: How many time you will spend on the phone? If you only plan to use it as emergency, you'd better try pre-paid phone card. If you use this as your primary phone, compare the plans service provider have, which one is best for your usage.
3. Phone: It's your personal choise, most phone sold tody are tri-mode with digit communication capability (E-mail, on-line), etc. This is purely depends on you.
By the way, I heard Roger is GSM, and Bell is CDMA. This might help your choice as well...