Actually, I think they're just trying to figure out how to charge you for it

Fact:  Cell phone use on airplanes is prohibited because of concerns about interference with the avionics.

Fact:  Airlines are beginning to allow broadband Internet access through a special connection that will not interfere with the avionics.  Yet, the airlines have blocked access to Skype and other VoIP software.  (Joe Sharkey explains in this NY Times essay).

Claim:  They're worried about people talking too loudly in the cabin.  As Sharkey explains:

Airlines should allow voice calls, at least for business travelers, one woman posting on Computerworld.com said, adding that she thought businesspeople could be counted on to use the service in a "respectful, quiet manner."

But that optimism isn't shared by others who assert that, as a blogger elsewhere put it, "these Type-A business people are the worst in bellowing on their cellphones." Another comment on Computerworld.com supported the in-flight blocking of Skype and similar programs "until phone users learn to speak in a normal conversational tone instead of shouting."

Fact:  Those in-seat phones that charge outrageous rates are still there, but their future is in question now that Verizon sold the service to LiveTV.

Drawing the appropriate conclusion is left as an exercise for the reader.