[bri3d]

AGPS refers to a specific set of technologies, MSB where the almanac and time seed is provided over the cellular network, and MSA where the unit sends GPS data to the AGPS server and the server solves for location using whatever data it would like (which can include a multitude of corrections).

I think what you're referring to with cell tower triangulation (and also WiFi location, etc.) is generally referred to as "hybrid location service" and is usually done at a higher level (ie - in software) using AGPS as one input to a sensor fusion algorithm.