I think you dont need script to automaticly connect to 3G when you start some program (like browser)

Settings - Internet connection - Edit networks - <3G internet/mobile data> - Use automatically

When you start browser it should auto connect to a 3G network that you selected. At least it how it work on my phone.

And if you need to turn on/off background connection you can use kkarioja script ( you can find it here: http://talk.maemo.org/showpost.php?p...&postcount=810 )

But if you want to use a different connections by diferent apps, it is problem we can try to solve... Honestly, I had no need to think that way so far. Of course I think it is not possible to use different connections simultaneously.