Sounds like something didn't got installed as it should be.
You could browse your SD-card and look what files can be found, there should be a file named 'voices' and all voices should be installed into that file.
Each voice has three files of its own:
1 .bmp file.
2 .chk file
3 .vif file
If either one is missing, possibly the voice wont work.
Also make sure, that both application and everything else is installed on SD-card. Maybe (just a thought, not saying u did so

) u installed them seperate (internal memory and SD-card), maybe the voices are on the internal memory instead of SD-card???
Anyways, the following link gives you a suggestion (in 2 steps) how to manualy install the TomTom voices on your device.
URL -
http://www.tomtom.com/support/index.php?Language=1&query=voices&FID=3299
Otherwise, these are the following steps I recomend:
-make a back up first, before deinstalling or formatting from SDcard (just in case :tongue

- format or deinstall everything of TomTom from SD-card
- reinstall application, a region_map, and of course a voice
- install latest update of the application of TomTom:
Title 'Updates TomTom USA'
URL-
http://www.tomtom.com/support/suppor...D=3&Language=4
As a small company, TomTom has been having huge no. of work for the USA-continent, when it comes to support.....let's hope they will improve within short terms.
You can always look at their support-section of their webpage for FAQ's
I work a lot with TomTom products, so I know a few things. Let me know how the suggestions worked out for you.
Good luck!
PS; Did you check if your sound and voices were enabled? U can check this in the main menu (page 1/3), tap on 'Change Preferences'.......Sound and voices should be enabled, when navigating..