3.1mbps is too good, only if it doesn't disconnects.
one can even trade with basic internet connections, like the non broadband one,
I've used vodafone USB stick and one good thing about it is it never sleeps when its idle.
however the speed is between 120 to 160 kbps only as 3G speeds are yet to come on private gsm operators.
I've used voda stick to do trades using powerindiabulls and ODIN, no issues if those are the only thing you have open. if you need to do parallel downloads you should use a broadband only.