Our family used AMS for undergrad tuition payments. It is a great way to avoid loans. No need to pay the full tuition price at the beginning of the semester.
The monthly payment is the yearly tuition cost divided by number of months you choose to pay (usually 8/9/or 10). I am not sure how they make money other than the sign-up fee (?$75) and if your monthly payment is not in their office by due date they charge an extra $25 for that month. I think you can have payments automatically taken out of your checking account to avoid any of those fees.
AMS has a list of colleges that "belong" to their program.
There are other programs/companies that run this type of tuition payment. Another one has the initials TMS. (sorry i cannot remember what that stands for).