Dial Up. Constant "No Carrier Detected". GOING NUTS!

[Fahrvergnuugen]

I can't figure out what is wrong with my Dual G4. The modem related kernel panics have ceased in past OS updates. Right now, I am at 10.0.3. If I try to update to Explorer 5.1.1 using software update, sometime in the middle of the download, my modem disconnects with a -264 error.
I usually let this download take place over night because of how slow it is. But when I try to reconnect after having it sit with a -264 error for several hours, I cannot reconnect to my ISP. I get a No Carrier Detected error.

I know its my G4 because my G3 laptop has no problem connecting [rulling out the phone line and the ISP]. I've even been able to duplicate this error in OS9. I tried calling myself with both my G3 and my G4. When I answer the phone with the G4 calling, nothing can be heard. When the G3 calls, you can hear the modem trying to handshake.

Shutting down the G4 for five minutes or so usually solves the problem. I reboot and then I can connect first try. Does this sound like the modem is not resetting properly? This is a really frustrating problem. Any help would be greatly appreciated.