If you have Nextel dialup modem or Packetstream service, there is an easier way to configure your "modem" to work with your mac.
In previous entries, I've given you a modem configuration script tailored for the Motorola iDen series of phones for use with Nextel. It turns out that there's a much easier way to go.
Buy the Nextel USB cable and get either Packetstream service or dialup modem service. They claim that you need their software and that it's only supported under Windows, but it works just fine with OS X.
Plug in your USB phone cable at both ends and go into the network preferences. It should notice that you've added a new device. Set it up with either a dialup destination or, for Packetstream, with a phone number of "S=2". Then flip over to the "modem" tab and tell it you have a Sprint PCS Vision modem and not to wait for dialtone.
That's it.