You have to keep in mind that GPS and cellular are two different systems. some smartphones can use tower triangulation to help localize the signal, but that is not available to all phones at all times. Also it really depends on the phone as to how efficient the GPS unit is and how much it relies on cheats like tower triangulation. Or mapping cheats, like sticking you to the nearest road, or going by dead reckoning when it looses signal, and correcting when it gets back.
Kuuto, they probably are a case by case basis, they would work well with some phones, not others, or might just be acting like antennas for use inside truck cabs and the like. As far as I know there aren't any phones that don't have a GPS that have enough power to run a map system. I think they were more of a transitional product (like GPS units for laptops) that don't really have a wide market anymore. Most phones get good enough GPS performance, but there are so many phones on the market that its impossible to make a blanket statement. I have a galaxy nexus, and its decent. but somedays it just doesn't know what its doing.
Given that most people don't use maps or GPS on the smartphone outside of an urban center, I would never trust a smartphone as a wilderness GPS unless I had fully tested it, and was sure that it was doing what it was supposed to be doing (and that includes after every update) Because the usual consequences of a GPS failure in a city are not that bad, there is more chance for a system to go wrong (for a week my phone's GPS decided that I was always 500 yards west of my actual location, not at all helpful) The design imperative just isn't there.
