ive noticed my blackberry which has gps takes a long time to pinpoint my location, it starts at about 1500 metres away and works in from there, most of the time it is so far out i might as well be in south africa!
this is when im inside and the built in gps doesnt get a signal or isnt strong enough. outside its different.
but what this shows is that you shouldnt rely on the triangulation method too mush as its nowhere near as good as a dedicated gps.
the bluetooth ones are excellent and u can place it very near a window when your inside and that will help pick up the gps signal.
go to ebay and find one for less than £50 and you should be ok with that. or buy a dedicated gps sat nav, phones are good for calls and texts etc but not so good for gps.