You are wrong.
An aGPS system has two separate functions.
The first is a traditional GPS satellite system, that works that same as other GPS systems.
The second is a cell-tower based system, which is used when GPS lock has not been achieved.
It is true that cellphones generally have smaller, poorer, antenna than dedicated GPS units, but that has nothing to do with the aGPS function, it is a hardware difference.
These devices can be used as GPS units with no SIM cards installed, so no cell connection.
Originally Posted by tompe
Assisted GPS can also mean that you download data from the net to help get the first fix.
aGPS seems to mean various things.
ie OneStar can be assisted (You have someone on the line assisting you)
Originally it meant a cellphone used towers to locate itself and out of tower range had no bearings at all. There are many interesting stories about people trying to navigate with these aGPS devices.
I will say this one thing.
If your device says aGPS only, then it most probably is cellphone oriented.
If it says GPS it has a chip.
Now can a device with a cell connection and aGPS also have a GPS (standalone) chip. Of course.
Some of the good GPS units (not cell phone) actually use something akin to an inertial guidance system. It doesn't have spinning gyroscopes, but it can tell if it is slowing down in a tunnel system and estimate how fast it is going even without satellite connections. It does that by remembering how fast it was going when it entered the tunnel, and since it knows the tunnel's dimensions, and has an idea of the speed of the vehicle RELATIVE to the initial speed, it can tell you where you are.