TiVo uses the Worldcom network to connect to the outside world. Try calling the phone number your TiVo dials and see if it's still a valid number. When you dial people, do you have to dial the area code? Many areas around me are now forced to do that. Perhaps you have to update your TiVo with that info?
You can also try adding
,#034 prefix to your config. That will force the TiVo to connect at a speed slower than 56k to see if your line conditions are suspect.
You can also try using
Worldcom's PoP Finder to check for new dial-ups in your area and possibly find that the number you dial now has been put out of service.
Of course, you could always get a TurboNet. I highly recommend it. If your TiVo modem is fried, 'electriclegs' on the TiVoCommunity forums can replace the modem chip. It is also possible to use an
external serial modem with the TiVo.