There may also be some limitations on how long you may stay online. Busy access numbers during prime hours are not unusual. If you are just a casual user or very parsimonious, it is definitely worth investigating. One characteristic I have found is that at first the services are quite fast, but as more users access them, they slow down for a while. This is until the provider adds more capacity.
Some people are surprised that they are available without charge, but so is network television.
As you sign up you have to give some demographic information about yourself. If you enjoy playing with the Internet, these ISPs are worth a look. When I see information on the Internet that I like to keep, I copy and paste it into Notepad. Recently I have been getting a long error message when I try to paste which says that I don't have enough memory to complete the operation. I am told to quit one or more applications.