OTOH, why would you need to be always online "with a good bandwidth"? tasks that benefit from being always online (updating RSS, instant messaging, ...) don't require much bandwith in the first place... and if they run while the device is in your pocket, you wouldn't notice that they're slower than usual.

then when you plan to surf around or download something, you can switch back to 3G for a while (or maybe have wifi anyway).

so... yes, it could be a reasonable strategy to use 2G as default.