I use 'Straight talk' (with AT&T based sim) in the US. It is not a lot, but still is cheaper than just being with AT&T and also gives me much more high speed data per month. Problems? The high speed internet might not be as reliable as AT&Ts (I feel I get 2G at more places when compared to AT&T), but mostly it is good.

US is really costly when it comes to phone bills. One of the most advanced countries in the world, and can't give cheap internet.