You are misinformed. Assisted GPS is simply a feature that reduces the time-to-first-fix of GPS. Triangulation from cell towers exists, but nobody calls it A-GPS.
I've used the iPhone 3G, 3GS, 4, and 4S extensively in the wilderness. Every version since GPS was introduced has been "real" GPS.
I'm not talking about cell tower triangulation, I'm talking about offloading computation to more capable hardware located remotely. It exists:
http://en.wikipedia.org/wiki/Assisted_GPS#Modes_of_operation
I can't find anything about chipsets that only do that, but I'd be surprised if nobody had ever done it.
One is the bad kind where GPS only works when you have a cell signal. It offloads a lot of the processing to the cell tower. This is used by cheap phones to comply with FCC requirements for location reporting for 911 calls, and isn't found much elsewhere.
The other is the good kind where it grabs the almanac off the network when possible for faster cold start times. This kind still works fine when you have no connection, it just takes longer to figure out your location when you turn it on, because it has to download the almanac the slow way.
They're basically unrelated except for the name, which is confusing.