In regards to the above theory,
I am not knowledgeable about such things, but the modem connection should not be made astable by the type of traffic performed over it.
I've had a lot more success by adjusting my modem's error-correction protocols to match those of my ISPs. It seems many modems default to no ECP, and the unidriver supplied with Windows doesn't have the hardware-specific codes to adjust them. Result: poor connection that will drop at the first error.