My suggestion:
Consider the case when player A and player B are near each other, and they talk through chat. If no one of them has a walkie-talkie, then both know that they are near each other. However, if both of them have a walkie-talkie, they do not know if they are close to each other or not, i.e. they cannot distinguish "normal" chat from "distance" chat over walkie talkie.
I've had quite a few situations where this knowledge would have been beneficial. I would suggest adding some markup to the chat, either change the color or have some prefix, so that the chat would look like: Player A (Walkie-Talkie): blabla.
So that people know when they are actually using the Walkie-Talkie.
Please consider, as its not hard to add I guess.
Example situation:
We have a team of 8 players. Player 1 has a walkie-talkie and is far away from the 7 others. The 7 other players are all close to each other, but only one of the 7, player 2, has a walkie-talkie. Now player 1 says something which is addressed to all players. But only player 2 will get the message, and since it will look like "normal" chat, he might think that everybody else has read the message. Which is a mistake. Even if he knows that the others don't have walkie-talkies, just because it looks like normal chat one usually thinks that everybody can read it.
If player 2 would know that this was a message sent by walkie-talkie, he might figure that he has to forward the message to the others.