The frequency that they use for talking is know as the aircraft emergency frequency (also known as guard), which is a frequency used on the aircraft band reserved for emergency communications for aircraft in distress. The frequency is 121.5 MHz for civilian, also known as International Air Distress (IAD) or VHF Guard.
When the Commander brings Finn's body back to the site of the massacre, she refers to the location as "TonDC". This is short for Washington, DC, which is on an ancient sign they pass just a few minutes before and the remains of the Lincoln Memorial (that Lincoln is named for). Many in-series locations are short for the actual location names they represent.