Introduction and background information:
SpeakOn relies on SAPI5 voices already existing on your computer. SpeakOn does not come with any voices itself.
Microsoft Windows XP, Vista and Windows 7 come with a SAPI5 voice installed as standard.
If accessible products are installed on your computer, it is probable that these include additional SAPI5 voices which would be available for SpeakOn to use.
Some SAPI5 voices are available for free to download from the internet. More information on these and commercial voices is available in:
Tutorial > The Manager > SpeakOn speech and messages settings > Installing additional voices
In general, high quality voices need to be purchased.