I was forced to use ISDN for a while when I first moved. Basically it's phone lines. They contain a dialup 64kb line. You can get 2 and have 128kb connection. They are good and bad. For gaming I had no issues...I had a very good ISP that I connected to and actually pinged better with ISDN than I did with cable...for download it stunk like a 56k modem.
The cost was the same as 2 phone lines which I had anyway because I wanted a seperate data line. Then I also had to pay an ISP. Nice thing about the dual is that it will drop one channel and let your phone ring when there is a call. Then when you get off the phone it picks back up...so you go from 128 to 64 back to 128.
Call the local phone company & see about availability and pricing (as well as some ISP's). Back in the day you had to pay based on connect time. I had a flat monthly rate...same as a phone line.
Oh, another drawback is that, unlike a standard phone line, ISDN will not function at all if your power goes out. You also can't use a regular phone connected to the ISDN jack...you have to hook the phone into the ISDN modem.