Trial begins on the use of satellite tracking in Singapore

[CityFarmer]

GPS is pretty useless in built-up areas. Normally, the phone tracks via either the telco 3G stations or wifi hotspots through triangulation.
Turning off GPS only reduces one source of location information.

GPS only works if u are in areas if you can see the sky. The rest of the covered up areas, u need to have internal coverage. Something like 3G yes but i doubt they are going to use the telco's equip due to security.
If are they are going to install new equip? Building all the infrastructure from scratch is no joke, meaning all the covered car parks , tunnels, expressways in sg.
Looks it would most pro be done by ST electronic again. (would they use neratel products?)

The method is already been used widely, the technology of Assisted GPS (A-GPS). No new infrastructure needed

From wikipedia

"Assisted GPS, generally abbreviated as A-GPS or aGPS, is a system which can under certain conditions improve the startup performance, or time-to-first-fix (TTFF), of a GPS satellite-based positioning system. It is used extensively with GPS-capable cellular phones"