Virgin Mobile has them beat.
For $30 a month*, you get unlimited** (2.5 GB throttle) data and text, and 300 minutes voice. Activating tethering is an extra $10 a month, I believe. (It's free if you have an Android and the right app, like I had before my 4s - my only complaint with switching.) They run on the Sprint network, so YMMV with service.
* $35 a month if you don't give them a CC to auto-bill
Not really.
It's sprint so data is slow. GSM has better data speeds over 3g especially with hspa+.
T-Mobile 's 4g is even faster than their faux G aka hspa+.