Factory H3 NAV

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I'll address both questions.
Kowal...
I don't believe the NAV for the H3 has been released for production, and if it is not released for production, it cannot be ordered from GM Service Parts. Possibly, they are considering ordering a NAV for an H2.
As to is this possible if a NAV is available...maybe. I have studied the wiring schematics for both the optional radios and the NAV. It appears, but I cannot confirm, that the only addition needed for the NAV is the installation of a separate antenna. (The antenna is even questionable, since the combination XM/Onstar antenna that comes on the H3 is also capable of being used for NAV; however, the schematics and illustrations show an H3 with a NAV will have a separate GPS antenna.)
(The flat part of the XM/Onstar antenna is used for to receive the XM signal and the GPS signal required for Onstar. The little screw in antenna is the communications antenna for Onstar.)
The remainder of the NAV system is built into the NAV head unit.
Again, I can't verify this since our H3 with a NAV is no longer around, and I only looked at the front, never removing it to look at the rear connector points. But, GM likes to keep the connector common, and the wiring diagrams say they are common.

Hummertech...
Yes, want a part number, I can look it up in the GM online parts system at work.
The part number on the radio in many cases is not the part number that is used for service; sometimes it is, but never trust this number. On the GM dealerworld system, accessed by dealers and GM employees, if you enter a part number into the system, and a new number has been released, it will show the correct update number.
You can call the GM parts division's help desk in Grand Blanc, MI, for part numbers of items you cannot locate on the GM online parts system. I would guess 90 percent of the time the online parts system has the part number (be it incorrect or correct), sometimes the part is not shown. Usually, the problem with the parts department is they can't find the part due to their failure to find it in the system. The parts people in Grand Blanc are extremely familiar with where the part might be in the online catalog. Sometimes, the system the dealer is viewing is not updated as often as the system the Grand Blanc people view.
Part numbers change like a weatherman changes his forecasts...constantly. For example, if a different supplier supplies a part, and even if the part is identical, a new part number might be issued. Another example, GM does a recall, the new part number has to change so that they know the old (bad) part is never used again.
If GM switches from Delco plugs to NGK, a new number is issued, etc.
Another reason why part numbers from the factory are not the same as service parts is the way the factory receives the parts. A good example is the rear suspension/brake corners. In most cases the rear axles with the brakes installed are delivered to the factory in one assembly, and the part number for that assembly is for factory use only. However, for service, all the parts of that assembly are issued a service parts number and that is what you look up in the online catalog to find the correct part number.
(I can note here that Saturn still issues printed parts catalogs for shipment to the Saturn Retailers.)

However, I go back to my original, if the vehicle cannot ship with a NAV because it has not been released, service parts usually will not have the part, and if they do, they should not be shipping it to the dealers since it is not an authorized part. Usually service parts are shipped and package to GM service parts prior to the vehicle being shipped, but they are not turned on in the system until authorized.
The GM parts catalog might show the part available but it is not available. Reason for this is the parts catalog might have been produced in May, the vehicle ships in June, but not all options are available; however, the catalog will show the parts since somewhere along the line the option is available, and at that time GM wants the service parts available if there is a warranty problem.

Hope I didn't mess everyone up.