This driver works with my PCtel 56K Flex PnP modem. It comes from Zoltrix-www.zoltrix.com/FMHSP56p-spects.htm.
My PCtel modem did not work until I installed this driver. The chip on the Zoltrix modem is the ONSpeed chip and on my Pctel modem the same chip. The date of this driver is May 26, 1999. Windows will indicate that this driver is not for your PCtel modem, however, install it anyway. Unziping is required before the install. It works for me.