Just the FACs please

I have a question about FAC operations in Vietnam. When a USMC got a
radio call for help, could he vector in aircraft from all services, or
were only USN/USMC aircraft at his disposal? Also, did Army ground
troops have the capability to contact any FAC in the sky regardless of
what service was flying them? ie. could Army soldiers call up a USMC
FAC? I'm just wondering how well-coordinated the ground/air was, or
if it was service-specific.