Okay thats good, it means you're on the right track. I also had trouble using the comms after take-off. When easy communications is ticked off in the gameplay options (e.i. using realistic comms), you have to use RAlt \ once in the air to contact someone. I'm not sure why exactly but that's how it is. If remapping the \ comms to TAB worked, maybe remapping the RAlt \ to something else will work as well. You can find it under the Cyclic controls.