Been lurking for a while, but though a post was in order...
Network-based positioning is used by many OEMs to get around the fact that some operators have not implimented their own Network Based GPS. It also enables devices that do not have a GPS chipset to provide some for of LBS.
The device can still be located fairly accurately in terms of longitude and latitude. The application can use the location API to acquire the location (longitude and latitude). In network-based positioning, the data comes from a server that contains a database of Cell ID's and their location (example, supl.nokia.com, Ericsson MPS)
The server has information about the cell ID and its longitude and latitude. The device asks the location over the network and the server pass from the data base to the devices.
Been using NBP for a while... seems to do the trick :-)