T-Mobile only gives you 2GB before they cut you down to EDGE speed (some plans only give you 200MB) - and they don't even have real 4g.. Verizon had a "true unlimited" plan a couple years ago that some users were grandfathered into as long as they stayed on their current plan with the same phone (or paid full boat for a new phone), but they will not renew contracts with unlimited. Any new or upgrade contract has the 2 or 4GB bucket and then its like $30 per 2GB when you go over. So unless you plan on keeping your current phone forever, don't count on having that unlimited plan forever. You will lose it if you upgrade your phone.
Sprint is the only one left with "true unlimited". Its going to be very interesting in the near future with the Softbank acquisition, and new rumors of a possible buyout of T-Mobile.. Sprint may become the ones to beat, with a fresh cash infusion to throw into the LTE buildout.
Also, unless you are paying $30/mo extra for the Mobile Hotspot feature (which is NOT unlimited, BTW) it is a violation of your terms of service to use it (ie: using hacked hotspot/tethering apps on rooted phones).
Most people get away with it because they are smart about how they use it - because today's apps are bandwidth intensive and it is not unusual to use a few gigs a month on the phone anyway. But you can bet your ass if you start using it as your home internet connection and streaming Directv over it they will catch on quick and they will terminate your service. People doing dumb stuff like that (torrents are another) are why the companies put cap/throttle policies in place to begin with.
Sent from my Galaxy SII using some Tappity Talkity thing.