@smegheadz,

I'm not sure I understand your question. GPS is basically downstream. A GPS receiver receives the GPS signals transmitted off the satellites.

What you had as far as I can understand was a system with a GPS receiver and some transmitter sending the location data to somewhere.

The transmitter itself is not a GPS but whatever proprietary radio signal you are using. The transmitter is however not sending data to the GPS satellites.

So with your N900 you can of course receive GPS signals from the satellites, but in order to be able to receive (sniff) things that are sent by your containers you would need to know how the stuff is being sent. At most you could get lucky with the FM receiver, but it's very unlikely that you are using FM for this (it's mostly illegal in most countries).

If I've misunderstood your question, please feel free to clarify it!