Call center. You might need some experience doing customer service already, but call centers are the way to go. It is stressful, but there is usually a way to move off the phone within a year or two. Call centers generally pay really well because the turn-over is so high and they need incentives to keep workers there longer. Again, I repeat, stressful, but if you can stick through it for a year and get the hang of it, you will get promoted to a spot off of the phones. I now work in a correspondence part of customer service answering written and email inquiries- world of a difference.
I am 22 and make a really decent wage for someone with only a high school diploma. You can PM if youd like to know how much. I got my first call center job through a temp agency in San Diego, and when I moved to Seattle, I directly applied for the job I am at now (with a health insurance company). I had good benefits at both companies, paid vacation and sick days, retirement options, etc. Just dont go for an outbound call center, doing collections or sales, that will really drive you crazy. I would look for something in-bound, customer serivce oriented.