Below is a message i received from View Ranger digital mapping for mobiles support. As a number of people could be considering this option after the positive review in Feb TGO magazine i thought i would share the content. If you are not a techie like me, it might be helpful. (Thanks to View Ranger help guys)
You WILL need some sort of GPS (internal or external Bluetooth) for the phone to work with ViewRanger.
Phones with internal GPS (like the Nokia 5800) work perfectly fine. It could be argued as a Bluetooth GPS costs more (on top of the cost of the phone) it will be more accurate, and battery life on the phone would also last longer (as it is not powering the GPS). But you can buy a phone with internal GPS and still use a Bluetooth external GPS anyway.
Please see our documentation on Bluetooth GPS if you are considering buying one as there are things to watch out for.
Here is our compatible phone list;