To upload a sketch, we have to change the positions of small jumpers on XBEE/USB selection pin headers,
and to activate RF communication, we have to change it again.
Removing it and putting it over and over again, I was about to go insane.
But this switch:
(linkman SS-12D00G3 slide switch) helped me.
I removed the pin headers and soldered the switches like this:
Now I can select the XBEE/USB connections at once, I will never get angry with the jumpers
I hope the slide switches will be implemented on official XBee shields.