Aye! I was with Verizon for three years, but after the BS they tried to pull over Network Neutrality and their firm stance on forcing me to buy a data plan--despite using minimal data (that I only used because I was paying for it, not because I needed it)--because I had an outdated smartphone, I decided to switch. I chose T-Mobile for the exact same reason, getting the pay-as-you-go plan. (They also said they don't force the data plan on smartphones, which I believe, but I got a dumbphone so I couldn't test that.)
Unfortunately I fumbled the switch over and had my number ported too early, meaning I had to pay Verizon's cancellation fee. This revealed to me just how horrible their customer service was (until then I'd had mostly pleasant experiences with them the few times I had to call) in trying to get my last month properly pro-rated. However, now that all is settled and done, I paid $200 for signing up with T-Mobile (half service, half for the phone+taxes), plus an extra $20 to Verizon over what I would have paid for my final month; that was back in October, and since then I haven't had to fill the phone once, meaning I've so far saved $170 (Verizon was approx. $80/mo). I still have >$50 on the phone, too, so this works great for someone like me who makes few calls/texts. And, theoretically, I can easily go to a monthly plan (still no contract) if I think I'll be using a lot in a short time frame, then back down to pay-as-you-go (I imagine I'll lose what minutes I have left when I first change, though.)
 WARNING TO EXISTING VERIZON USERS: If you have a contract and wind up in a similar situation as I (porting the number, cancelling the service, being charged the cancellation fee, and then trying to get time paid for pro-rated back), you must explicitly call and tell customer service that your phone number was ported or they won't consider it "cancelled". Their customer service tried to wiggle out of pro-rating me because I didn't do that, despite calling on three different occasions from the ported number, confirming on all three calls (if quickly) that I had full changed over, and them already charging me the cancellation fee. In the end I got my money, but it was a pain in the ass because their customer service kept saying they would do X but not do it or only half do it.