Using multiple connections together

I posted this in Software section but no reply hence posting here.

I have MTNL wired broadband and Tata Photon Plus EVDO datacard. I wanted to know if there is a method of utilizing both the internet connections together.
For example if i download any file, can i utilise both the connections together (and thus get higher speed)?
Normally when both are connected, the OS randomly utilises any one automatically.
Solutions working either for Windows7, WinXP and/or Ubuntu will be better.
Any difficulty level and working on terminal is ok.

Thanks in advance