LG VX-8600 / AX-8600

I travel a lot, and needed an external antenna to get a signal in some remote areas. After hooking my AX8600 to my external antenna, it now will not receive a signal without being hooked to the external antenna in my truck. Alltel rep says it's the phone....get a new one. I just spent $300 getting the external antenna setup, etc. put in my truck. Is it software or a manual switch that switches between external and internal antennas? Anyone? Any help is appreciated. For now at home, I had to break out my old crappy razor v3c to use till I get my LG working again.