I'm getting ready to drop Verizon after close to a decade of use. The $100/month bill is starting to take it's toll. Not "bad" service, but I am lucky to get a bar or two at home or at work. Everywhere else it's great. I mostly stuck with them because I am eligible for their unlimited data plan, but within the last year I've mostly been using wifi and it's not worth the $30 charge. I also don't like that they only offer a 450 minute plan as their lowest talk plan and it isn't that cheap ($59.99).
I have been looking into Republic Wireless. It's a service that buys coverage from Sprint, but most of the service (including calls) is run through wifi to cut costs. The biggest downside is that you have to purchase the phone (Moto X $299 & Moto G $149). There is also an issue that they don't have short codes (
http://en.wikipedia.org/wiki/Short_code ) programmed in, but they claim an update is on the way. On the plus side, their plans are dirt cheap compared to the major carriers with the most expensive being $40/mo unlimited talk/text/4G service/5GB data (that's not over wifi).
Verizon was my first cell phone carrier and it's been hard to let go, but I think it's time.
If you're interested in Republic, you can find them at
https://republicwireless.com/ex/