In America, you need to keep your phone off between takeoff and landing. But on foreign airlines such as Emirates and Ryanair, you're welcome to make calls in-flight. Better them than us.
These airlines have overcome safety concerns that have kept phones off in the air before:
On-board equipment regulates the signals by routing them via satellite to the correct point on the ground. Passengers with standard international roaming service can make or receive calls or text messages just as they would on the ground. They are billed as usual by their mobile phone providers.
That's all well and good, but just because you can do something doesn't mean you should. Allowing people to talk on their phones in the air will turn a quiet flight into 6 hours of being trapped next to some guy on a conference call. Luckily, Congress is working towards banning in-flight mobile phone use just for that reason. Please, please, please make that happen. In-flight Wi-Fi is amazing, but in-flight mobile phone use is the work of the devil. [NY Times]