Xasthur, you can *always* talk to people on range, you dont need to tune that channel. Just hold down F12 (instead of T) while talking.
The V channel (tunable vox) is for other channels. Squad (red) voice, Mission. Most Squads also have a number channel (in the 100-199 range, thats on team only).
The channels 200-299 are also voice able and go cross teams (ie players from different teams can tune it and hear/talk/type on it). The most common one is 200 for text (in replacement of the disabled All channel).
For those number channels: only players that have tuned it can read it. And they can only HEAR it if the have it tuned in V chan.
You can also tune another player to voice private (by writing his name into the V chan box).
You can also use the V chan as another text channel (ie type on it). Just use the
SHIFT \ shortcut to open radio.
Channels that can be read even though they are NOT tuned: (All), Country, Range, Squad, the CM channels (gold and blue) and HTC official channel (turquoise).
More on
radio usage from Net Aces.
Edit: With the new setup, the red Squad text channel is cross arena. You can also page another player with
.p gameID . This will send a private text (white) to the player in question.