A reader commented that he had gotten Mobile Skype running on his handset. After trying some more, I'm still unable to do this. I also see that the Skype Developer Zone lists this as a known issue with Skype Mobile:
On PocketPC phone editions audio comes out from loudspeaker, it is not
transferred to phone speaker. To avoid using loudspeaker, we suggest you to use
wired headset. This will also give you better overall sound quality in Skype
In many cases if you have bluetooth headset connected to Windows mobile
device, it is not possible to use it for Skype calls. In most cases you will not
hear anything, or most of the text is cut off.
If anyone reading this has managed to use Skype on a Windows Mobile device over the phone handset, meaning as a regular phone call not over the loudspeaker or PDA headphones, please comment with more details!
Until further notice, I conclude that Windows Mobile gives programs an API to the speakers and mic that only works on the loudspeakers or PDA headset and not through the phone.
All that said, I still like the idea of Skype Mobile on my TyTN, especially since I live outside of the USA and call the USA a lot. When I can listen to Grateful Dead tunes while switching back and forth between local cellular calls and international VoIP calls, and while checking my e-mail, I'll feel like I'm living a convergence life.