If only ISDN is available, know that it is very solid. The 3com ISDM IQ modem has a speed doubler program that gves you in real time about 200K using A and B channels. It expliots a routine in Csco routers. I loaded it and it always worked. This is the only ISDN modem that takes advantage of this hidden feature. You will also need a card from Lava company Hi speed Serial port. When you step up the speed, your normal ports can't do 100% of the capability of the modem when speed is doubled