Actually, you CAN hear enemies talking, and its really badass. Just check out some of the shack tactical videos, some of them even have enemy soldiers begging to surrender after being cornered, its great ^_^
Arma VON is very impressive considering its just an addition added in a patch (although it was supposed to ship with the game, but it doesnt make it any less impressive). Its bugs are worked out and in-game (no the breifing screen) it works almost flawlessly!
There is even changes in volume depending on whether your character is talking locally or on the radio. Examples:
On GROUP channel, you can speak only to the members in your squad. HOWEVER, you will still be heard by non squad members, but your voice will be in a quiet volume, because your character is talking normally over a "radio" to your squad members.
When you use the DIRECT channel, your character speaks very loudly and can be heard by everyone for a prety good distance, depending on obstructions and the environment/weather. Everybody will hear you, even enemies, and it will not broadcast over the radio.
Using VEHICLE channel uses the current vehicles internal radio system and broadcasts to only the players inside YOUR vehicle, although you can use DIRECT channel for this too for unimportant conversations in the back of helicopters before entering the ****.
Using SIDE channel talks to your entire team (which is spammed and is very annoying, picture that talkative commander in PR who wont shut up, now times that by 20+ players, you get the point

)
Using GLOBAL talks to EVERYONE ON THE SERVER (!!!) which was a prety dumb thing to include, why they included that for public players I will never know, it should only be avaliable to admins... There is plenty of times where you will hear horrible screaching/breathing/someone eating cause they left their VON on and arent paying attention. Theres been several times where I had to rip my headphones off cause someone entered the server and tried to use their VON and it wasnt configured properly or something and the piercing screaches that came from their mic was deafening... still gives me the shivers thinking of it.... *shudder*
What
Arma VON is greatly lacking is a channel for LEADERs. I have no idea why they didnt include that... Something simular to the commander channel in
BF2 except all squad leaders and the commander can hear each other. Because of this, if you want any organised play you will NEED to use teamspeak.
Also whats a very strange decision is there is a volume slider for the different VON channels using "radio" which is great. But for whatever reason the LOCAL channel uses the same volume adjuster as ALL THE REST OF THE EFFECTS in
arma... meaning a large majority of players cant hear the LOCAL channel well at all because of their effects volume being low, which COMPLETELY negates this awesome feature as most players dont use LOCAL von because of this simple oversight.
One thing
arma players WONT mention to folks coming from PR that is prety important to know is the fact that realistic PVP
arma is basically non-existant in a public form, so most players on the
TG server just use SIDE or GROUP channel cause they are only ever fighting bots and there is little need for a high degree of organisation when fighting a predicatable computer. Not that fighting an AI is not challenging, but needing to change plans quickly to counter a sly intelligent manuever by the enemy is simply not a worry in
Arma... your more worried about the AI making that amazing 300 meter headshot or miraculously seeing you through that thick brush.