While I have used USB modems I would never call a dial modem good enough for today's owners. Folk today will not accept what was accepted back then on dial up.
The USR models have always been fine but then you have folk that can't accept the reliability of dial up. This no one can cure and why consultants do not do dial up today.
I have been trying to set up "Incoming Connections" on Windows XP Pro with USB dial-up modem. I don't have any problem to set it up. But I was never able to get it working. So far I have tried USRobotics USR5637 and FILEMATE USB Modem CX made by Wintec. Did anyone ever get any USB modem working for "Incoming Connections" on Windows XP Pro? We have to do this because customer's machine is not allowed to be on the network or internet. So we have to dial-in to troubleshoot issues. Thanks!