[nobody314159]

You need a receiver in the phone that can phase track, which costs 50x as much as the simple GPS chip they fit.

You also need either a lot of storage locally or a fast data link between the base station and the rover - phones actually have both of these but they cost money

[jrockway]

You need a receiver in the phone that can phase track, which costs 50x as much as the simple GPS chip they fit.

So, $0.50 instead of $0.01? :)

[nobody314159]

I think Phase tracking GPS chipsets are still pricey - outside surveying applicatiosn there isn't much demand.