Navigon is very good with turn by turn voice. I used just the East Coast of the US. It is slightly pricey but pretty good. But I did really like the voice input on my Google Maps on my Droid X. Maybe Siri can integrate and give you voice input on the IP4S.
iOS has much better navigation scene than Android. Android has that free Google Maps that requires data but other than that what has it got? The same apps are lower quality on Android.
Navigon is very good with turn by turn voice. I used just the East Coast of the US. It is slightly pricey but pretty good. But I did really like the voice input on my Google Maps on my Droid X. Maybe Siri can integrate and give you voice input on the IP4S.
This +1.
If you're going to do it and you think you'll use it, get something like Navigon. Overall, the combined price of the phone (16gb) and the app is less than what you could spend on another stand alone GPS device.
If you're only going to need it here and there, go the free route.
+1 on MotionX. It's only .99. I did purchase the optional turn-by-turn voice guidance ($19.99 for 1 year), and it's completely worth it. The turn-by-turn package includes spoken street names, so that's a huge plus.