All vehicles use their radios to communicate through various channels/frequencies when simply speaking is inconvenient or impossible due to distance. Every vehicle also has a private channel that they only share with close friends or other vehicles they trust.
Teams usually have a shared channel that all of them use. They switch frequencies every once in a while to prevent non-teammates using them after they were kicked out of the team and to avoid enemies randomly stumbling upon them and using them to spy on the team. Not all teams do this, inexperienced ones often haven’t realised the importance of this procedure yet.
Many experienced teams have developed some sort of “code” for radio communication during battles. It’s deemed crucial for keeping the communication concise and the orders clear. The exact code varies from team to team; they use whatever works best for them.
Channels and Frequencies
It’s possible for a vehicle to be tuned in to several frequencies at once, but connecting to frequencies they aren’t tuned in to at the moment takes several seconds. There is only a limited number of frequencies, which makes it possible for a patient tank to just spam connects in order to detect an unknown used channel. Depending on the quality of the radio, the connect time and number of parallel frequencies can be improved to a certain extent, making it easier for scouts to try and detect the frequencies another team uses, given enough time.
Vehicles can also communicate nonverbally over their radios by sending special signals. This can be used to send silent messages, which take longer to transmit than spoken words, though. They also don’t carry tone or emotion of the sender, which is sometimes bypassed by adding special signals to the message that denote the intended tone. This sort of communication is very useful when there’s the need to not make a sound, for example to not give away one’s position to an enemy during a battle.
Another use of nonverbal signals is quickly determining an allied vehicle’s location, which is done by sending a request and receiving a ping.
Differences between tanks and planes
Most tanks, unlike planes, have the habit of accidentally switching to a less formal way of radio communication, especially when excited, scared, or angry. It’s just in their nature, as the codes they are equipped with by default are mostly limited to their individual movement and shooting/targeting processes. They have to consciously learn and stick to their team's agreed-on code. Planes traditionally use Brevity and generally have no problem sticking to it closely, but using “tank codes” is alien to them and they slip up just as often as tanks do when using them.