Mobile internet/ Home Phone & Broadband HELP - UK only -?

[stanley]

I am looking into getting a mobile internet Dongle but dont know who to choose it is for doing my online coursework.
I have heard things about people who have had massive bills because going over the limited of downloads but i wont be download i dont think, is 3gb big for the internet?.
it must be a uk company I.e 02 or T-mobile.
Or i was thinking of changing my Home phone / broadband supplier im on BT at the moe & am not happy with the customer service has anyone got any ideas of who to go with for both or either question ( Dont mention sky either)

THANKS