I don't know... yet. As part of a R&D project we are developing a prototype to show in a few months time. The chosen platforms for the mobile device are Android and Maemo, and to be able to use both a gprs data connection and a WiFi one at the same time is an essential requirement for what we want to do.

When we find out how to do it, I will tell you (although I don't know if it will be practical enough for and end user).

Greetings.