I recently bought a couple of these GSM/UMTS gateways, which are really quite cheaply available on ebay: Cheap GSM CSD/Fax hardware
They use a SIMcom 5320E module for GSM communication, pair it up with a ATmega128 as the main processor and a Conexant 56k modem.
I wanted to have a wired/mains powered modem to do CSD fax and data calling, so I tried to use the included USB port.
Sadly, the gateways are a special SKU meant for lifts (made by Kone apparently).
I was able to use the Windows XP configuration utility, which is actually quite nice (when trying to use it for the intended purpose):
But there was no way of communicating with the modem itself.
After a closer look at the board, I noticed an unpopulated footprint at the bottom, which can be populated with a USB hub IC.
This USB hub would then enable a PC to use the native USB communications feature of the SIMcom module as well as the FTDI FT232 USB-serial converter (to talk to the ATmega/main application processor).
So I just went ahead and soldered the 2 D- and D+ lines from the SIMcom module to a USB connector:
which then results in this very nice sight:
