Success: Two-way phone call with Treo 650 in Linux

Now that I have a VOIP account that can make unmetered calls to mobiles I decided to try having a play with getting two-way phone calls working from Linux on the Treo 650. I turned on the phone part in Palm OS, booted this kernel and reset the power on the gsm module with:

echo 0 > /sys/devices/platform/palmt650-pm-gsm/power_on
echo 1 > /sys/devices/platform/palmt650-pm-gsm/power_on
echo 1 > /sys/devices/platform/palmt650-pm-gsm/wake

I then fired open minicom and opened /dev/ttyS0 at baud 460800 without flow control. I then connected the modem to the network and entered my subsidy unlock pin:

AT+CFUN=1
AT+CPIN="xxxxxxxxx"

Once connected, I called my phone via VOIP and then answered with the ATA command:

RING
RING

ATA
OK

At that point I opened up a few terminal windows and started fiddling with ALSA. I first started playing some white noise so I could heer when I started transmitting:

cat /dev/urandom > /dev/dsp

I discovered you can divert PCM to be transmitted by the phone using:

      Master Mono: Enable, set transmit volume
              PCM: Enable, set PCM volume
PCM Play to Phone: Enable to route PCM signal to the phone module

After some more fiddling I routed the microphone to the phone. The labeling of the Mic controls in the ALSA driver is rather strange but here are the key settings:

      Master Mono: Enable, set transmit volume
Mic Select Source: mic1=handset, mic2=headset
            Mic 2: Selected mic volume
   Mic 1 to phone: Enable/disable handset mic 
   Mic 2 to phone: Enable/disable oheadset mic
   Mic 20dB Boost: Useful in speakerphone mode, you can talk from quite a distance.

Mic 1: [irrelevant?]
Mic select:  [irrelevant?]

After that I managed to get the incoming audio going out the handset earpiece with these settings:

         Master: Enable, earpiece volume
Master Left Inv: Enable
          Phone: Seems you don't need to unmute, but need to set volume.
Phone to Master: Enable
            Aux: Set a high volume (weird stuff happens if low)
    Out3 LR Mux: Master Mix (mislabeled, it's actually out2)

I've made an ALSA state file for working two-way phone audio with the handset.