Coagie,
Jehrler, Even if an aircraft is equipped with satcom equipment to relay ACARS, it's a common mistake to assume, that it's communicating directly with a satellite. Instead, it communicates with a ground station, that relays it up to a satellite. Many areas don't have a ground station near enough to the aircraft, to get a good enough signal. Although technology exists, where commercial passenger planes could communicate directly with satellites, there's a lag in implementation, because it has to be tested to make sure it doesn't cause unexpected problems with other systems on the plane. Then standards have to be agreed upon, so it's usually a long time, between the time a technology comes into existence, and it's implementation on an airliner. Even changing the type of coffee maker in an airliner's galley takes years!
If that is true that is very interesting as it means that calling these SATCOM is really a misnomer. It also makes me wonder why this would be a useful addition for ETOPS aircraft as they would seem to spend a fair amount of time over open and base station free areas?
I just assumed (yes, I know) that when someone discussed SATCOM they were discussing an iridium like service (with the attendant high high costs).