ACARS/Satcom
Vandelay,
As has already been said, ARINC and/or SITA are the best source of information - they are the major suppliers of ACARS services via VHF and satcom, as well as retailers of satcom services for passenger and flight operations use. They use the Inmarsat satellite network, and support additional ACARS services over satcom including ATS applications such as ADS and CPDLC using FANS-1 (or FANS-A if you prefer the Tolouse variant).
There was an article in Flight Deck International last year (from memory) which described all this. Apparently some operators are using satcom ACARS in preference to VHF to get around congested VHF channels, particularly in Europe - costs are similar.
Satcom voice use for flight operations and ATC is also increasingly popular - it is a real improvement on HF voice, but so is almost anything. I'm told it's the preferred method for contacting Kabul ATC for those who find themselves in that airspace.
Hope this helps
Freq SLF