[bri3d]

A-GPS can run in Mobile Station Assisted (MSA) mode, where the device sends raw GPS data to the A-GPS network and the assistance server processes it. In this situation, the assistance server can use whatever precise cell site location and ionospheric correction data it wants in its processing, although this is more of an "exercise left to the implementer" and I'm not sure sure MSA mode is even very common anymore.

[ianburrell]

I think was only a brief window where MSA was used, when phone processors were weak and cheaper to have limited GPS chip. Now, GPS chip do everything onboard and are included on radio processor or main processor. Plus, phone processors are powerful enough to do GPS themselves.