First, make sure your WebTV isn't trying to dial a local number. You can do this by unplugging the box,
then plugging it back in. Once you turn it on, it'll either ask if you've moved or start dialing toll free. If it asks if you've moved, say yes.
Once you're done, plug the phone line in and let the WebTV dial. With any luck
you should properly dial in and be taken to registration.