1800ed
My undestanding is that the 3G models use assisted GPS the other models do not have GPS.
Assisted GPS uses mobile and / or broadband signals to improve the cold start time which becomes usually only a few seconds.
It is also my understanding that without assistance (no 3G or WiFi) the GPS will operate, well at least as long as there was a recent fix. However I have seen reports that if the almanac has not been updated for some days then the GPS will not cold start and no position will be given (for example if on a two week passage across the atlantic).
Whether or not this is an accurate description I am not certain; please clarrify if you know otherwise.
I am guessing that you dont actually need to have a contract with a 3G provider (just the micro sim installed) to enable an asisted fix - but I also dont know.
In short exactly what the parameters are for an assisted fix is not clear; it would be intereting to know.