Like others, I've experienced the lockup of dial-up internet connections when fax receive is active. I recently tried Page Sender in hopes it would fix the problem, but it has the same problem as does enabling "Receive faxes on this computer" in the Print & Fax System Pref.
I've found a correlation but not the cause: If you attempt a dial-up connection within roughly 20 seconds of waking from sleep, the connection will fail. The system recovers from this failure gracefully. However if efax is running, pppd will hang. Attempts to kill the pppd panic crash the computer (Mac OS 10.3.5 and probably earlier version of 10), so my only recourse is to restart. The manual workaround is simply to wait 20 seconds before connecting, but with others using the computer, this hasn't worked well. I tried several ways to solve this problem with AppleScript, but my final solution is user friendly and totally automatic.
A shell script uses scselect to disable dial-out during the critical period, then re-enable it when the danger of hanging pppd is over. It uses a special network location setup with the modem disabled. This mechanism is very fast, but assumes one normal location. Others may be able to design a way to restore one of several possible working locations.
Since there's only a problem if efax is running, the script first checks to see if it is. It then uses scselect to switch the network location to one that does not have the modem enabled. It then sleeps for 20 seconds, then selects the normal network location, re-enabling dial-up connections.SleepWatcher runs the script when the computer exits sleep (wakes up). My script usesCocoaDialog to present a message and progress bar, so the sleep time is broken into one second increments.
Here's the script; it's called WakeupPPPchecks in my case. Don't forget to give this script execute permission:
[sudo]chmod +x WakeupPPPchecks
[/sudo]
CocoaDialog provides a great progress bar and worked better than AppleScript for status reports in the face of changing user environments, but is certainly eye candy. Thanks to the many posts on Mac OS X Hints which led to this workaround.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040901023017510