T-Mobile just flipped the switch in 50 markets, doubling it's 4G speeds. This will give you 42Mbps download speeds, if you are lucky enough to be in one of the markets covered. This is, of course, theoretical speeds, so expect real world speeds to be a little slower. This still surpasses Verizon's LTE, and crushes AT&T's '4G'.
Users have already reported seeing speed increases on their devices. If you want to take full advantage of the new speeds, you can pick up the new Rocket 3.0 Laptop Stick tomorrow. This USB stick will retail for $99 after a $50 mail in rebate, so long as you are willing to sign up for 2 years.
With blazing fast 4G, and new devices such as the HTC Sensation 4G, it is really unfortunate that the merger with AT&T is all but inevitable. For a full list of places blanketed by 42Mbps of speed, hit the source link.
-Andre