The problem with cell phones isn't RF interference, as modern phones put out so little and modern airline computers are well shielded enough as to make that not really an issue.

The problem with cell phones on the plane is that the towers and switches on the ground can keep up with a phone that is, say, on the freeway, where it is handing off the device every few minutes. Multiply the speed of the airplane by 8-10x, and those handoffs become that much more frequent. At that frequency, they do more than just drop a signal - they cause substantial load increases on the hardware and software that control them. That leads to outages for those on the ground. That's on top of the problem they have just getting - and holding - a signal TO your phone 7 miles up in the air.

During TO/LD, having everything turned off and put away means the crew will be able to get your attention during the riskiest part of the flight. So don't be a dick about it - just do what you're told. I WILL rat you out. I don't want to have my safe egress from a crippled aircraft (assuming we aren't a large fireball) dependent on someone who won't follow simple crew instructions, and neither does anyone else. So grow up.