Best thing to do is setup a SIP client/service (e.g. Vonage, Gizmo, MagicJack, etc) and use that to make your phone calls via data, and most likely if you need another data connection, hopefully it will also connect. I had my Vonage Softphone client working (sort of...couldn't call every number, not sure why) via 3G and WiFi, using the Sipdroid app. All the issues were credential and port settings related, but the concept is successful.
My DROIDs were returned, but I guess if you can stream internet audio, and then browse the web, you should be ok. Come to think of it, I believe that worked for me before, so you should be ok.