MDM6610

This is the Qualcomm MDM6610 baseband chip used in the iPhone 4S.

Baseband Firmware
The firmware for the baseband chip comes in Trek-X.X.XX.Release.bbfw files (with X being the version). The BBFW file is just a renamed standard ZIP archive and contains a couple of .mbn files which are all digitally signed with a certificate from Qualcomm. Qualcomm's Senior Engineer Shital Mehta is involved with the programming of the firmware. The amss.mbn file is an file:

OSX file command output
file Trek-1.0.11.Release/amss.mbn /Trek-1.0.11.Release/amss.mbn: ELF 32-bit LSB executable, ARM, version 1, statically linked, corrupted section header size

iPhone 4S
1.0.11  5.0     (Build 9A334) 1.0.12  5.0.1b1 (Build 9A402) 1.0.13  5.0.1b2 (Build 9A404) 5.0.1  (Build 9A405) 1.2.01-1 5.1b1  (Build 9B5117b)