Actually you can install TTS starting on Froyo 2.2
I installed Loquendo Susan TTS. Her voice is MUCH better than the stock Pico TTS.
just go to mobilism and they should have the susan loquendo TTS apk file. It works but I have to manually select Susan TTS every time i want to hear her voice.
This works on Navigation, as i hear her voice daily. her pronunciations are quite clear and gets enunciations accurately
for instance, she says 'el camino real' but with correct intonation in spanish way!