First, this is a legitimate number from Ft. Sam Houston (medical division). It can be placed on the automated programming or be live. It is programmed to call those with pending medical appointments to remind an eligible subscriber of a future appointment.
With regard to actual calls on the live line, I think someone (not necessarily a military member, remember there MANY civilian employees working within the confines of DOD), is bored with their overnight shift and is calling for their own entertainment. That should be unacceptable but remember, civilians are well protected by their union AND it would be quite a difficult challenge to prove it's happening. It would take a kind of "class A" type action to level a charge against this employee.
Why the assumption that it was a civilian employee? Odds are if the phone line is located at Ft Sam, it could be a civilian employee, a DOD contractor, a member of the military, it could be lots of people.