Recently Bing app for Windows Mobile has added free turn by turn directions.  TTS is used to read out the address during navigation.

http://www.bing.com/community/blogs/search/archive/2010/05/11/updated-bing-app-for-windows-phone.aspx

If you have a windows phone, have a try with it.   How do you feel the TTS voice quality in it? Please comment!