Believe it or not, most people don't do voip, and most still use POTS over cell phones. Are there unlimited plan with POTS? Yes; but most people are on the same plan they've always been on. Most people don't like change.

This is also why I use SipDroid on my android. With my kids, wife, and I all on Verizon, all calls to each other are included. Using SipDroid on my android, I can have a very inexpensive cell phone plan. I have a family share plan for all for of us. It's only 500 minutes, and we NEVER go over the 500 minutes. You can definitely get unlimited in anything if you want to pay for it. I prefer not to pay for things I don't need.