I originally bought an unlocked Samsung AO2s for a trip to Europe. It is dual sim and I picked up a sim card in Europe which was also really cheap and it worked great. When I returned to the United States I decided that I wanted to keep using the phone which was very capable and stumbled upon the EIOTCLUB sim card. I actually use a google voice number for making phone calls and I can do anything else as well with the sim card.
It is almost unbelievable how affordable this system is. I can get a year's service with plenty of data for around $200. The google voice number also works really well. It rings to the phone but also rings to a wall phone in the house and to my wife's cell phone as well. It does confuse people when they call and she answers, but we love it.
I can't imagine being tethered to any of the major phone companies for thousands per year. This does take an unlocked phone and a few brain cells, but will save you 75% or more per year.