The Western Space Missile Centre (WSMC) HF Net operates the following frequencies for emergency contact relating to munitions:

USAF MARS HF PHONE PATCH NETWORK

K The Air Force MARS phone patch system is a network of auxiliary HF stations authorised by DoD to provide phone patch service between US military aircraft and ground agencies and ships. Allied military and other aircraft are also provided support IAW agreements and international protocols as appropriate.

General services provided by MARSRADIO are:
- Unencrypted official and morale phone patch services to DSN or commercial numbers
- Emergency assistance through phone patch or operator message relay
- Radio equipment checks
- SEL CAL radio equipment checks

Callsign: MARSRADIO

Frequencies:
- Primary 24H 13927
- Alternate 24H 7633.5
- Tertiary / CONUS Night 2300-1400z 4557

USSOUTHCOM

USSOUTHCOM is responsible for the force protection of U.S. military resources in Central and South America, and the Caribbean. SOUTHCOM is also responsible for ensuring the defense of the Panama Canal.

Callsigns:

Mainsail (HFGCS Puerto Rico)
4724
6739
8992
11175
13200
15016

Smasher (USSOUTHCOM - Honduras, Florida, Guantanamo, Aruba-Curacao)
11205
15025

Skywatch (US Army South ATC & AIC - Honduras)
8120 Secondary
11410 Primary
15790 Secondary

Below an archived copy of old USAF information for your reference. Procedures are largely similar in HFGCS.
(Specific base frequencies have not been varified since 2002):

Standard Operating Procedures (SOP's):
Authorized users may request service from GHFS station by calling "Mainsail". Any station in the net recieving the call will respond and provide requested service. Minimum service by all stations are phone patch and message relay service. Phone patch permits direct voice communication between ground agencies and aircraft/ships by electronically connecting telephone circuits or other voice channels to radio transmitting and recieving equipment. For pp: callsign, telephone number and location should be stated if known. 
When contacting GHFS for RTTY, global will designate and alternate frequency for the service. 
EAM messages are common on all frequencies, only aircraft with emergency or distress situations are to interupt EAM broadcasts made out by GHFS using the static words "PAN PAN PAN" or "MAYDAY MAYDAY MAYDAY". GHFS are not directly capable of Direction Finding. However stations can assist in DF by coordinating between various aircraft in the vicinity.

More often then not you will hear "REACH" aircraft requesting a pp to an airbases' AMC CP giving them a heads up about their load, passengers, estimated time of arrival and aircraft technical status. Almost always this pp is followed by one to the destinations airbase meteorological office to ask them the current or expected weather conditions before they land there. At the end of the pp to the wx shop on an airbase the pilot occasionally asks the meta man if he wants a PIlots REPort (PIREP) as an extra service, so the wx shops can give better forecasts on the weather for other aircraft and anticipate.

AMC Operations Center: The USAF Air Mobility Command Tanker airlift Control Center (TACC) at Scott AFB, provides worldwide service for AMC missions. Either TACC or appropriate AMCC can be contacted for airlift movement reporting or assistance through Global stations. Calls can be made out to:

Note: Also the Air Force Eastern Test Range (AFETR) can be contacted as back-up on 10780 (pri) or 20390 (sec) under callsign "Cape Radio". Furthermore a new station has stepped in with callsign "Puerto Rico".

352 SOG, Mildenhall, UK

The 352nd Special Operations Group at Mildenhall AB operates several aircraft. Operations are using the callsign 'Blackhat'. For HF they have a wide array of frequencies available although the following are mostly used:

USAF KC-135, Det Istres, France

After operation 'Allied' force the USAF(E) still maintains a KC-135 detechment at Istres/le-Tube, France. Operations goes by the name 'Riviera Ops'. Their HF Operations are taking place on:

Ramstein Airbase, Germany

Apart from the GHFS system, the 86AW aircraft based at Ramstein have a specially formed HF service at their disposal which can help them to make the missions a succes. The communication unit is based at Ramstein and is using the callsign 'Metaphore' and uses the following frequencies:
6819
6870
7919
14682
15082

Giebelstadt, Germany

Brindisi Airbase, Italy

Identical to Mildenhall, the Special Operation Squadron here has a HF usage. Operations here are using the callsign 'Promenade'.
5590
10596
14511