We have utilized Straight Talk for over 5 years and have little if no problems with them. We both (DH and I) have smart phones, so we have to pay the $45/month plan. It totals $46.87, including taxes, etc. for a total of $93.74/month vs. the $178 we were paying for AT&T service.
Our Straight Talk uses the Verizon network and anywhere that gets Verizon service, you will have service. We also get 3G of data for that price and any data over that, we get at 1G speed. It's still unlimited, however much we use. That being said, we don't watch movies or seldom watch videos, so we don't go over that amount.
We have had a couple of instances in our travels that we haven't had any service, but those areas also have little/no Verizon service, so it wouldn't make any difference which one we had.
We will NEVER go back to one of the major carriers. It's just too easy to sign up for the automatic payment each month and not worry about it.
ON EDIT: You do not have to purchase one of their phones if your phone is compatible. You can go to www.straighttalk.com and check the "bring your own phone" program. Enter your phone's ID# and it will tell you if it's compatible or not. If you just want a new phone, just purchase one that meets your needs.
If you just want something for an occasional phone call, if you purchase it online, it can be pretty cheap, sometimes, even free.