IF you have coverage they are fantastic. I absolutely love their plans and I save a ton over the others. I left Sprint because their price rose to be closer to the other big carriers but their speeds were attrocious. Their 3G is TERRIBLE and their Wimax/LTE was the speed of Tmo/AT&T 3G. 3G is just bad for all the CDMA carriers.
With the money I save when I do travel where I don't get coverage on vacations sometimes I can pick up a prepaid sim and toss it in and hop on AT&T's network and still save a ton of money. It isn't voice that's an issue /w T-Mo in most areas, just data gets to be horrible outside of most large city suburbs.
Their Hotspot devices are awsome too... My mother has T-Mo and barely going online so I signed her up for a 3GB hotspot device... costs $10 a month total, not bad.
On top of that, T-Mo is playing it smart /w their advertising. I always laugh when I hear AT&T advertising their Next plan /w 4 phones for $160 /w 10GB. That doesn't include phones even. T-Mo slaps them and throws out 10GB for 4 phones for $100... that's $60 lower for the same thing!
It's about time the market got shaken up by someone, because the other carriers are ripping everyone off big time. T-Mo's CEO saw a huge opportunity to make huge changes that made them stand out in a big way and people are moving over in mass. Now if they could expand their coverage /w the extra income, they could do even better.