The errors you see in your mobile phone's positioning are due to signal problems (reflections, etc) and the relatively limited capabilities of the cheap GPS radio in your phone. A decent GPS receiver with a well-positioned antenna will get a highly accurate clock.
http://www.nytimes.com/2000/06/15/technology/pentagon-lets-c...
The errors you see in your mobile phone's positioning are due to signal problems (reflections, etc) and the relatively limited capabilities of the cheap GPS radio in your phone. A decent GPS receiver with a well-positioned antenna will get a highly accurate clock.