I will reply to this thread later today with the files attached to the thread that you need for the silent voice.
To get it on the iPhone you will need an application on the PC to send the files across to the iPhone I use something called "Disk Aid" its not free but it certainly doesn't break the bank, about $6
This application lets you see the files on the iPhone in a Windows Explorer style view, you can also copy/ delete files on the iPhone. You need to find the main folder where the TomTom application is stored, in there will be a sub folder called "voices" delete one of the existing voices but make a note of the number the file will be dataXX.chk (where XX is a numeric value), leave the 03, 04,05, 06, 07 files alone as this is where the English speaking voices are. Probably best to remove something like "Manderin" - will let you know which number that is when I post later.
With the replacement file on the iPhone start the TT application and go to where you select the voice, choose "Manderin" and it will use the file containing the silent voice.
The other suggested way of doing this is to mess around with the contents of the apk file then re-load the whole application but this method no longer works, the DiskAid method works fine though and is a way of installing third party POI files to the TomTom iPhone app - Just a shame that there is very little custom POI support in the iPhone app to make use of the additional data - Mike