The built-in antenna on many CF GPS' are wide enough to block the Axim's headphone jack so you can't plug anything in there. E.g., the Pharos and GlobalStar CF GPS' (off the top of my head).
The great thing about the Ambicom CF GPS is that the antenna doesn't block the headphone jack. Altho the built-in antenna sticks out quite a bit when the CF card is installed...
cbuchner1 wrote a review of the Ambicom CF GPS here:
http://www.aximsite.com/boards/showt...ht=ambicom+gps
(Sorry for the big URL, I'm a newbie.)
Hrm, can't remember exactly, but I think Pharos (or some other company) has a model that can detach the antenna from the CF card. Or, of course, you can get a GPS which uses a mouse antenna instead of the kind built into the CF card... (I don't own a PDA GPS, but I think some mouse antenna-only models might restrict GPS use to inside a vehicle with cigarette lighter power jack.)