We know the ARM RVCT Compiler delivers a higher code density and significantly better performance than binaries produced using other leading tool suites. As binary size has a significant impact on the final cost of phone hardware, RVCT is used by phone manufacturers to compile binaries for ROM. The signature files here are presented with following toolchains that can support iPhone Basebands and their platforms (chipsets):
2.2 3.1 4.4 ThreadX sigs
Files on iPhone 4 firmware can pickup upto 800 functions when all the sigs applied.
iPhone 4, iPhone 3gs, iPhone 3, iPhone
http://www.letsunlockiphone.com/iphone-ida-pro-signature-files-baseband-reversing/