Do mobile phones with built in GPS (Blackberry 8310, Nokia N95 etc) actually use real GPS or do they just use the phone service providers cell network.
I don't want to have to buy both a GPS and a new phone if one unit will suffice. On the other hand I don't want my GPS to cut out as soon as I am out of network coverage.
Yes indeed, those phone and others that generally claim GPS, do have to use the proper Global Positioning System (ie satellites). Some other phones, most notably the iPhone, use cell tower triangulation (not very accurate) in combination with wi-fi networks (more accurate) but this falls short of the precision of GPS. These 'virtual GPS' systems will improve over time no doubt but for now YMMV. Also note Apple do not sell this as a GPS feature.
You'll need to bear in mind 2 things when using GPS on a mobile phone. You'll pay for the data downloading when using the mapping. For example, if you've never been to the place you're at before it will download the map of that area when you ask it to look for where you are or where you're going. Also with the N95, the talk feature is not included and you have to buy that seperately if you want the driving instructions spoken to you. I don't use my N95 for GPS for this very reason, it's too expensive for me!