Well, we all know that there is no official solution for Turn-by-turn navigation on the iPhone, yet. Why? Well, let's have a look at Theiphoneblog. Some points they make sound quite reasonable, but in my opinion only at first sight.
Licensing conflicts? Well, yeah, Apple doesn't own the data provided by Google. Who said that an Application made by Apple would have to use Google's data?
SDK agreements? Well, that is no point at all because Apple made the agreement and they can change it any time. Beside that: the agreement applies to 3rd party developers only, not Apple.
A company like TomTom would be afraid of less hardwae units sold? Sorry, but that's complete bulls*. TomTom, like many other, already sells their navigation software to be used on cell phones. It runs on Windows and Symbian based handsets. So, why shouldn't they sell it on the iPhone as well?
Well, I don't have any better idea myself at this time why there might be no Turn-by-turn on the iPhone, but I still think that it will come soon, maybe this year...