I just got mine working. Most of the help I got came from reading "nabi"'s posts over on the Navitol.com forum.
Even though I have a PDA, he said that TTS voices only work in PNA versions. I can verify that none of the PDA versions (even one that claims to work) worked for me. There is a PNA version out there that works with my phone called Nav N Go iGO8 R3 series v188.8.131.52975 (May 11 2010)
The system requirements are as follows:
Microsoft Windows Mobile or PNA device, operating system 300 MHz processor, 64 MB memory, QVGA or VGA touch screen display
Operating System: Windows Mobile / WinCE
I had to use a data.zip file from one of the PDA programs I had tried to get it to work.