Iridium seems to be the network of choice of most professional / commercial users, rather than the Thuraya system which is much cheaper to use but whose geographical coverage is limited and whose reliability can be pretty poor (IME).
However I don't think any satcomms network has a monopoly on voice quality or indeed reliability - regardless of pricing. A friend of mine has had an Iridium phone installed in his turboprop, wired properly to his intercom/headsets, and has called me from FL250 or whatever, and the quality was so poor one could barely make out anything.
My guess (as an electronics engineer with a lot of comms experience) is that satelline networks work OK if you implement a very robust protocol which does bulletproof error detection/correction. TCP/IP (internet access) does this of course, for data, or perhaps VOIP if you are paying $$$$$ for a high speed link, but no protocol will protect against the link simply breaking somewhere in space, which seems to happen quite a lot. In these cases the local end (the phone or the computer) thinks all is well with the call but nothing is coming through.
I'd be interested to know how ACARS over a satlink is implemented. Does it use a dial-up call, or is it some kind of "always on" GPRS-like service? With dial-up, one would typically be dialling into a private server. With always-on, it is nearly always going to be an internet connection.