While using cell phones on U.S. commercial flights is still a no-no, the Europeans have decided it's OK to blab away once your flight is above 10,000 feet. I've always felt the U.S. ban on inflight use of cell phones was more motivated by financial and social issues than for technical reasons. As cell phone use became widespread in the 90s, the major carriers stood to lose money from those seat-back phones that charged upwards of 6 bucks a minute, so they weren't in any hurry to approve personal cell phone use.  As for technical issues, the studies I've heard about, including some performed by the major airframers Boeing and Airbus, have not produced any conclusive evidence that cell phone use interferes with the aircrafts electrical or electronic systems.  (If there are still technical concerns, then there really should be an comprehensive technical study, including extensive testing, that involves all parties and experts: airframers, avionic manufacturers, electronic engineers, government regulators, etc. To my knowledge, such a study has never been undertaken.) If anyone was concerned, it was the FCC, which regulates radio transmissions in the U.S. In the early days of cell phone technology, a call from an aircraft high in the sky could be picked up by several towers at once, possibly confusing the systems. (Though making a call from a mountain could probably do the same thing.) I believe the cell phone technology is more robust these days and many of those early concerns of the FCC have been eliminated.

It looks like there will still be some additional cost associated with using your own phone, as the airlines have to add  hardware to their planes to make all this work. This hardware will act as a conduit to relay your call through a satellite, and then down to the existing cell network on the ground.  The additional cost hasn't been estimated yet, but if it isn't a whole lot cheaper than those seat back phones, I don't think most people will use it. But you can bet the airlines, who are studying every additional revenue stream they can think of, will try to make as much as they can off of it.

After financial and technical issues, that just leaves the social concerns as a major impediment to allowing cell phone use on U.S. airlines. I feel many people like the fact that an airline flight is one of the last public respites from annoying cell phone use. Especially on long or overnight flights, it is nice to be able to take a nap and not have to worry about cell phones ringing or your seat mate babbling on and on about life's most insignificant details. I'm going to speculate that eventually there will be a compromise on cell phone use on U.S. airlines. You'll be allowed to use your personal cell phone or PDA, but only for the less intrusive text messaging or email, and only during the more benign cruising phase of flight, not during takeoffs and landings.