1118-2.pdf - Commands for Host-Processed and Host-Controlled Modems. This is AT command reference manual for the controllerless V.90 and V.92 USB faxmodems. These include the Models 2990 and 3090.
V250_CMD.pdf - This is a detailed file of the new V.250 commands used to support V.92 protocol.
These documents can also be downloaded from the Model 3090 support page.