You can change the voices on the S100 but the only english language voices available are us, uk and oz. I tried the spanish voices but my whole display (instructions, etc.) changed language!
If you mean custom voices or recording your own not available yet. But, satnav manf. are gonna have to provide some apps or nokia and android (maybe apple as well) are gonna kill em in the future.
Yes you can on s80. Just download a wav file & associate it with the POI's using Navman software. I added my own custom POI's this way & it works just fine.