Since I don't like to be without a backup modem, I recently looked at MultiTech brand. I purchased the MultiModem MT9234ZBA-USB unit as the specs mention is it compatible with LINUX. Well, I found out from the read me file that I would have to recompile my kernel and module to get it to work, so I sent it back and exchanged it for a refurbished (no longer made) MT5634ZBA-USB v.92 unit. This modem uses ACM0 instead of ttyUSB0 like my other modem did. It worked right out of box! It has a USB cable, not the serial to USB converter cable like my other two units used. The Baud speed in wvdial is recognized as 468000, or something like that, real high, and in order to connect without problems, I had to reset it in the wvdial.conf file to 57600. This is fine for our telephone line, considering that it has been torn up so many times by the tri-annual road grader and carelessly spliced by the telephone line repairmen numerous times, it is a miracle we get a telephone connection at all. I'm glad to have found a unit that works very well and wonder why MultiTech discontinued this brand? Highly recommended for dial up users.
Interesting read:
http://tldp.org/HOWTO/Modem-HOWTO-23.html
Edited to add this helpful page of changing the init string. Now I do not got the, "pppd daemon died unexpectedly" that I would get intermittently, but very frustrating as I would eventually get connected if I get redialing. I lengthened "modem timeout" to 85 seconds, changed ATZ to AT&F, and changed ATDT to AT W2 DT in the modem commands section, and in KPPP's connection speed, changed it from 57600 to 38000, or whatever the next lower speed down is. Mu husband told me to learn about the AT commands in the manual that came with my modem, but still, I wasn't sure what to use, so this how to did help and I am learning about AT commands at the same time.
http://www.4p8.com/eric.brasseur/modem.html
have dial-up, and have a US Robotics modem. 
