Hello Soul...!
You have some interesting suggestions there...

...!
This problem seems to have popped up since changing my 'phone company from "British Telecom" to "Onetel"...
I have just contacted Onetel, and they suggested the problem "may" be caused by the automatic inclusion of "Voice-mail", (1571), ie: "Call waiting", as part of their service...!
This voice mail service seems to store a number of incoming calls, waiting to be answered, (or not), until deleted.
I did not use this option on British Telecom, and the problem didn't seem to arise...!
In the case of Onetel, I wonder how I can prevent voice mail being stored on my telephone service so that any incoming calls will indicate "Line Busy" at any time that I am connected to the Internet via Dial Up...!
Is it something that can be achieved in the US Robotics Modem "Properties"...?
...ongoing..experiments...
Cheers all...!
Paul.
Note: This problem doesn't occur with Broadband, when 'phone calls and the Internet both "share" the same time.
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.