For me, it would end up being more expensive.
For $35/month, I get unlimited talk text and 5GB of data. This is grandfathered from VirginMobile (sprint/boost). There are no overages. If I exceed 5GB, then the speed drops. Comcast wants $12 for each GB. If you don't use much, you save but go over 2GB and it would cost me $36. That's more than I currently pay and for less data.
I also know VirginMobile has great coverage on the East coast. I've been with them since about 2006 and the only place I had no cellphone coverage was in Bar Harbor Maine. That was in 2009. They probably have coverage there now. (I had a phone with only cell service, no wifi ability).