I think that you're mixing up two things as you mention 3G. Bluetooth is only used to connect your tablet to your phone. Your phone's modem, dataplan and network coverage define the speed you can browse the net. If you want a fast wireless connection to your tablet, you should look into what kind of technologies (EDGE, 3G, HSDPA?) your carrier supports, and pick a phone that can use the fastest of them. Remember to also see the network coverage maps.

My carrier has 3,5G in city centers and heavily populated areas, and pretty good EDGE coverage elsewhere, so I picked Nokia 6120 which supports both.

Your frend's RAZR was slow, because it only supports GPRS data transfer, not because of slow bluetooth speed.