But will it allow third party GPS software

Google maps appears OK for walking around town (but so is asking directions), but until I can get some decent car based route finding / direction giving program on it I won't be buying one. Shame really cos other than that I really like the iPhone, it's just that GPS based route finding in my car is absolutely critical to me and if I have to keep my existing phone for GPS I may as well keep my existing phone for everything else.