A "winmodem" is a software driven modem and therefore cannot be "flashed". What you need is a .vxd,(virtual device driver)and an .inf,(device information file)to update your modem.
I could not find,(without paying out to 3com), an update for sometime until I stumbled upon this file.
I have an internal model 1125, but this
may work on othe USR/3COM products.
I used this on 95 and 98 without any
problems,connecting consistently at 48k, with good transfer speed.
If you are not familiar with configuring your device under windows,
e-mail me and I will assist you.