I've been using them for about 8 years, and am going to drop them when my contract expires in 7 months.
I got a new phone last year, with a new unlimited 4G data plan that is slowed down to 2G speeds after 2gigs. I rarely even use 1 gig. The main reason I went with this plan was because it had the free ability to use your phone as a free WiFi hotspot.
About two months ago, they took this ability away, wanted to charge me an extra $15/month to use it as a hotspot, and said I had to "upgrade" to the 5gig/month NONunlimited plan, which cost more. So not only were they wanting to charge me 30% more than I had signed on for, they were cutting back my data usage availability.
The free WiFi hotspot ability was written into my service plan, as was the unlimited data. They refused to honor both and just turned off the WiFi ability on me, and said I could sue them for WiFi rights if I wanted.
**** 'em. They lied, and changed my contract without my consent.