I installed OT/PPP last night, set up Modem and TCP/IP control panels. Using MacOS 7.6.1 on SuperMac C600L ("typhoon" motherboard) with GV Platinum Comm Slot, recently upgraded to 33.6 by firmware.
Trying to connect with PPP, I get dialog box saying "modem not responding. Check cables, make sure properly installed, etc".
I changed to every connect script I had available. Same thing. When using modem scripts that downloaded with the 33.6 firmware upgrade, the PPP control panel shows some commentary that system tries to talk to modem at 115kb, then resets to 57.6, followed by "(-640)", this last looking like an error code.
I can use this same modem to access CompuServe. Modem works fine.