Satphone A/G comms for FAR121.99 Dispatch/Pilots compliance

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I wonder if anyone could advise if the use of mobile hand held SATphones are an acceptable means of compliance to meet FAR 121.99 Communications Facilites with PIC and Dispatcher? I'm actually not even sure how reliably they would work on a flight deck. We're not in the US so no AIRINC. No experience here comments most appreicated. The aircraft do not have a fixed SATcomms unit, the are however ACARS equipped. Non ETOPS operation.

Thanks.