I prefer the gps on my phone. Gps on any smart phone is the same and it's already covered in my data plan on my iPhone 4 and was when I had the I3 as well and my sons phone is not an iPhone but a smart phone and is loaded with the same gps system.
I was about to say the same thing. The GPS on my 'smart' phone is pretty accurate and there are quite a few navigation apps out there for you to chose from.
My $.02 worth.