XP sp1 : problem w/ modem & hibernation

I have a workstation running Win XP sp1 with an AOpen internal (software based) modem. The workstation is used with a dial up account.
PROBLEM: When I shut down XP and leave it in hibernation mode, any phone call results in the system coming out of hibernation.

Is there a way to prevent this unintended wake up(other than disconnecting the phone line or shutting off the power supply)? I’ve heard that XP sp1 has a number of problems with modems, but I haven’t heard of many workarounds at this point.