i dont think you can add your own voices,only paid ones thru tomtom home
this is taken from a satnav forum which a member was doing the same thing
trying to add his own voices this is what he said
''I rang Tomtom support and asked why we were no longer allowed to customise our units, and they came straight out with to stop piracy, so we can no longer download anything from the internet and install it in your tomtom, they are locked and will be staying like that from now on. No more custom sounds, Poi's, Voices, bluetooth connection other than by phone no more connection to car radio, no SD cards or anything else, unless you buy it from them on their site, and they install it via TomTom Home.''
i hope this helps...