So I bought this, and a Piezo buzzer... and tried using this method here http://wiki.openwrt.org/doc/hardware....buzzer.method
on the T1+T2 pads to find out which is which.
For T1, the pad on the right, and for T2, the upper pad, produce the screeching/modem sound. Unfortunately they do so all the time (whether it's booting or not). The other two are silent all the time (also during boot).
I tried to blindly connect just GND and RXD but failed to get output for any of the pads. I got a single "?" for the lower T2 pad, and nothing for the others. Not sure if it's even supposed to work at all with just GND/RXD/TXD but that wiki page suggests it.
I was expecting to find a single pad that produces some noise during boot, instead I found two that produce noise nonstop and two which are completely silent.
So I'm stumped again. I just don't know enough about electronics.