At this point this .wav is only associated to a commando inside the .sounds files. There are all commands listed which the announcer can say, e.g. the commando axis_hq_compost_construct is associated to the hq_cpcon_a.wav resp. hq_cpcon_b.wav files, which say “Construct the command post!”. So I guess mappers can already use this .wav files for their maps.
Voice chats on the other hand are defined in the .voice files. So when you add a new command there, like this:
axis_need_fieldops
{
sound sound/vo/general/axis/hq_needfos_a.wav
sound sound/vo/general/axis/hq_needfos_b.wav
}
then you should be able to use it, BUT ONLY IF the server you playing on has the same modifications (even on an unpure server nobody would hear you, when you the only one with modified .voice files).
So, alter the .voice files, create a .pk3 out of them and find a server who will host this .pk3. Then you can use this .wav as voice chat (hey, this would be some kind of mini-mod, like “Skull Mine Flag(s)” or “TimeBonus”). This way you could also add custom voice chats.
Anyone can then bind this new command to a key (like the “old” ones):
bind x vsay_team axis_need_fieldops
I also remember shrub for RtCW had a command where you could play any sound, even from single player, when you had rcon access (I loved to play the zombie scream, scaring the hell out of the enemy).