What chipset is used in the 56k External USB Modem (MT9234ZBA-USB)?

The chipset is by LSI which used to be known as Agere. it also uses a Texas Instruments USB interface chip.

Information on AT commands and the User Guide for the modem can be located at:

http://www.multitech.com/en_US/DOCUMENTS/Families/MultiModemZBA/manuals