welcome to the 21st century
Some of the comments herein suggest that this is all new fangled stuff. Its not.
Emirates long haul 380's and the occasional 777 ER aircraft have had in air wifi and OnAir mobile phone roaming, so a couple of things;
1. Wifi is severely congested on an aircraft where I pay $10 for about 100Mb of data - its good for messaging but forget everything else, even browsing. i doubt many people actually use it so an aircraft full of kiddies simply won't be a useable service.
2. Few people use the mobile phone option, as others have suggested as the facility is punitively expensive (good news there then)
I share peoples concern over the yakking 16 year old with a phone welded to their ear 24/7 no longer having to STFU during a flight. They might get away with it once, but when their parents get the first bill, then roaming suddenly becomes no longer an option on their tariff and sweet silence returns.
The biggest concern for me if it takes off (pun intended) is whether its very long before the first cellular phone blockers go active onboard a flight and those are going to be a worse scenario from a safety point of view.