I have some RDS / TMC links on my site that you may be intrested in - there is also a link to an application for the PC.
Other sources you could look at are traffic master ( if you could hack the code from the shockwave version from the Vauxhall site ) ancd the same for the www.getmethere.co.uk site... pplease I think AA and RAC do the same ( not that I am a saddo that goes out looking for these things lol ).
I'm wondering if you could have an overlay of some kind with Destinator witch gives the ablity to change routes if needs be ? That WOULD be cool. Along with GPRS your away...