In theory, the "pes" driver in mess should allow you direct serial playback from serial(diserial?) input to speech output using the tms5220c; in practice this doesn't yet work, IIRC, some code is missing. I'll look into it later today.
As it is you can type stuff and you'll get random gibberish out the audio for every 10 or so bytes you type.
The PES driver is for the Pacific Educational Systems 'speech box', an rs232-to-tms5220c interface box. See http://blog.kevtris.org/?p=3
Scott M. Savage (inventor of the 'speakjet' pic18f1320-based speech chip) was selling the guts of one of the PES boxes on ebay a while back: http://www.ebay.com/itm/TSP5220CNL-Based...r-/271302556165
TSP5220c == TMS5220c