As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
REPEATED ATTEMPTS TO CONTACT DISPATCH VIA SATCOM WAS UNSUCCESSFUL. WE COULD HEAR THEM, THEY COULD NOT HEAR US. SAME RESULT WHEN DISPATCH CALLED US. WE TRIED BOTH CAPT AND FO COMM PANELS BUT WITH THE SAME RESULT. GROUNDED - YES. PERFORMED OPS TEST OF SATCOM SYSTEM REF B737-800 AMM 23-15-00-730-801. DISPATCH HEARD VOICE CLEARLY FROM ALL POSITIONS. NO HISTORY 90 DAYS. A/C OK FOR SERVICE.