Just remember, although the FAA no longer cares if you use a cellular device while flying, the FCC still prohibits the use of any cellular device while airborne (not touching the ground)! Here's the link to the applicable CFR:
http://www.ecfr.gov/cgi-bin/text-idx....1.1.2.8.27.12
The fine is up to $250,000.00 and cancellation of the device's ESN. The aircraft operator is responsible for compliance.
The prohibition applies to ANY radio transceiver operating in the terrestrial cellular radio spectrum, including the 2G, 3G, 4G, LTE, etc. data-only transceiver in your iPad, but NOT to sat-phone type devices that link by direct satellite comm.. I was told by an FCC investigator that the prohibition has to do with "frequency spread" and interference with cell tower switching, not any concern over navigation interference, which is why the FCC also still requires that all cell devices sold in the U.S. have an "airplane mode" that deactivates the transceiver while leaving all the other "pocket computer" functions enabled.
FWIW