When I was flying US domestic in the 90s, quite a few airlines (Northwest was definitely one) had handsets in the armrests. You could swipe your plastic through them and they charged $1/min - I assume they used a satellite link from the plane. I rarely saw them used, except for the occasional 30 sec "guess where I'm calling from".
You're unlikely to be able to conduct a mobile phone conversation in flight, because even if you could get a signal from the nearest cell (their aerials are angled to keep their reception focused on the ground, not at 30,000') you'd be travelling too quickly for a successful hand-off to the next cell as you moved out of range. I hate the idea of on-board picocells, as I spend quite enough time on trains listening to self-absorbed bozos broadcasting their business to the world.
But I don't have any safety concerns, since I'm sure that every flight with more than 100 people on board will have at least one (probably several) mobile that has been left on inadvertently, and ill effects are extremely rare (to say the least). None of which is an argument for disobeying the lawful instructions of the crew, of course.