Prometheus is no longer in business. These modems used SSC chipsets. Have a look at my notes for SSC based modems. They're all pretty much alike.

Prometheus

I finally found a good init string for the ProModem 144i!
Well, it works with the Quarterdeck Internet Suite anyway.

Reset 1: AT&F
Reset 2: ATE0L0Q0V1X4&C1&D3\N6S7=60

The &D3 causes the modem to wait longer before dropping DTR.
I have also found that a good generic string for most comm applications that require hardware flow control, data compression, etc. is:
AT&F&C1&D3\N6

Contact Information for Sierra Semiconductors (makers of Prometheus modem chipsets)
Sierra Semiconductor Corporation
Tel: (408) 263-9300 (San Jose, CA)
or
(503) 692-9601 (Somewhere near Portland, OR)
Fax: (408) 263-3337