Unwired offers a short list of commlink mods, most of which even seem to be useful. But where are the rules for upgrading the commlink's basic stats? SR4A, pgs. 222, 227 and 228 mention using the Hardware and Software skills to install hardware modules and code your own OS, but I cannot find a listing for upgraded hardware modules in the gear section. Do I have to build my own?

If you're referring to upgraded signal and response modules like I think you are, then the price listing is on page 222 in the "Hardware Upgrade Costs Table" Sidebar in SR4A. Personally I would have preferred to have those in the gear section, but what can you do.

BBB pg.222 Upgrading Devices and Hardware Upgrade Modules (SR4A)
BBB pg. 232 System and Firewall (SR4A)

Are you quoting page numbers in SR4A or the BBB?

SR4A version of BBB.

Thanks, omae, that's exactly what I was looking for.

btw, SR4a introed a rule saying that a system can not be improved more then 2 point vs its starting rating, iirc.