Here you can find some information about how to connect an Arduino to the iPhone using the headphone plug: http://forum.arduino.cc/index.php/topic,19648.0.html, that's probably the easiest and cheapest way to transfer data with low speed.
I'm curious, what kind of telemetry data do you transfer to the phone? As far as I know it already has accelerometer, magnetometer, gyro and GPS on board.