I used to believe this (and I'm a huge Mythbusters fan) until I joined the group I work in now. The problem is really really in how the cell phones are designed and where we're using them. If 250 people come aboard with working phones in their pockets, and we lock them all in an aluminum tube, they all start to work very hard to keep that connection with their cell tower.
Since output levels vary around the world, that may mean anything from 1mW to upwards of 2W. When you multiply that by 250, you're now outside of what Boeing certified to be safe from an EMI standpoint (Electro Magnetic Interference). So... the way the cell phone companies dodged the liability was creating "airplane mode". It was originally thought the plane would command this mode on, but it wasn't reliable enough, so the airlines dodge the liability by asking we turn everything off below 10,000'
Now, we've come full circle and our customers (and their passengers) want to be able to use all their toys. We solved the cellular problem by installing what is called a picocell and leaky feeder network on the plane. We trick your phone into thinking its on a network, so it never goes into high power. The next step (which is being done as we speak) is to get bandwidth to the picocells and provide you with your home network (ATT, Verizon, whomever) while in flight.
The limitation of "below 10,000 feet" is tricky and that's what the potatoes were helping to prove.
