Safely Airborne ie Gear up, Flaps coming in and you have time to talk on the radio.
We dont even start (757) to bring the flaps in to 3000 feet AGL which is way to late to start talking at most places. It tends to be Gear selcted up push the button on the flip flop to change freq.
The thing to watch for is people changing to departure once cleared take off and still sat at the end on the runway.