Also depends what all you want to do with your phone? If you want to remotely login to a windows machine, you won't be able to do that on a blackberry, but you can on the xv6700 device or any device running mobile 5.0.

Also where all are you wanting to travel to with your phone? Verizon is CDMA and so is Sprint, which I believe are just networks in the US and Canada. Nextel is on TDMA (old technology) Cingular/AT&T, T Mobile are on GSM, which will work in a lot of other countries. T Mobile will have the smallest coverage out of any of the networks mentioned above. I think I covered all of the cell companies.