Originally Posted by 1800ed
Thought I'd say though: With regards to the type of GPS Memory Map uses on the iPhone, the software is dependant on the hardware and the iPhones use an AGPS chip which I wouldn't rely on working too well in the air as it uses cellular data as well as GPS to determine your position; hence why I mention the TomTom cradle.
The iPhone is perfectly capable of showing your position with with cellular network turned off.
The cellular assistance just helps it get a fix quicker initially - it has no major bearing on on-going position updates once it has worked out its position, except again as an additional hint. If there's no cell info available, it can take longer to acquire the initial location/satellites, but it'll work fine from then on.
I've used my iPhone to track my flight path while it's sat on the RHS, and it has worked perfectly.
The Tom Tom cradle is apparently good in that it has additional GPS hardware in it, but it doesn't charge your iphone only maintains the existing charge, and there are reports it doesn't work with the iPhone 4. You'd also have to check if the GPS in the cradle works with apps other than the TomTom one.