Technology Review says cell phones on a plane aren't avionics risk: The author says that frequencies which cell phones would interact with avionics are for unimportant systems. But this disregards a key point in the IEEE Spectrum article that he's in part trying to minimize the importance of: that avionics equipment is designed with much lower tolerance for interference than the personal electronics and computer gear that might be used. The electronics we carry with us have much broader legal limits for out-of-band emissions, which can range far away from the actual frequencies a device is designed to use. Avionics on distant bands might be overwhelmed because it's not designed to cope with that much interference.
There's just no way to know without further study, and I don't see why further study is a bad idea in this case. Testing 100 cell phones on a plane of many makes, models, and ages while monitoring a range of avionics equipment (with and without a picocell on board) would be a great start. I'm willing to wait; what's the rush in getting cell phones used on board, anyway?
Further, this article states in an odd way that Wi-Fi costs $500,000 to install on a plane while a picocell will cost $100,000. Not really. What the author seems to have meant to say is that Boeing's satellite-based Internet access system that uses Wi-Fi for distribution on a plane costs $500,000. In talking to several firms that hope to win the air-to-ground spectrum auction that the FCC is running in early May, the cost per plane will be much closer to the lower number than the higher one. The weight of equipment and complexity of gear is much lower, and retrofitting is thus faster and easier, too.