There is a GPS library shipped with B4A. aGPS is a GPS feature which is automatically used by the GPS system of the device if it is available so there is no need for a special aGPS library.
Maybe on the Cell Tower Side. My Tablet also has an option to get location by Wifi networks. They are two different check marks and I can have the Wifi Checked and the GPS Unchecked. The GPS Object says GPS is off when only the Wifi option is checked. I'm curious as to how to make use of the WiFi side too.