I actually thought about that. Using cellular network for internet connection. Speed should be adequate. The problem is, I couldn't find a cellular chip that will connect to 3G, and is available to hobbyists. GPRS/2G speed is too slow for video streaming.
Thought about using a mobile phone to send text-messages with commands to the copter? IE go to gps-coordinate, stay at altitude, take pictures every x seconds and mms them back to the phone and stuff like that? Would be cool so you dont have to rely on the radio or wifi. I realize this is very much in the future but could be a nice addition if you succeed with the radio and wifi.
Yeah the perpendicular thing is not really a big problem. We can probably just live with the tiny error, too.
It's an interesting problem: orientation in space. I wouldn't worry about accelerometer chips not being perfectly perpendicular. You can apply a matrix transform correction in software.
How about some sort of compass and a sun angle detector? I realize a solid state fluxgate compass may be problematic in a noisy environment like a copter platform. But I've seen sun angle detector modules... just an idea that may be neater than gyros.