There isn't a global country channel. You have two voice based radio's to work with, "channel" and "range". The channel radio (Radio 5) will communicate with anyone tuned to it. Squad and Mission are pretty self explanatory, but you can also tune to a numbered channel, 100-199 is limited to your current country, anyone on your country tuned to that station will hear you. 200-299 is global, anyone on ANY country tuned to it can hear you.
The range voice (keyed with F12) will communicate with people in the same "room" although I will admit that I'm a little fuzzy on how the game determines what the room is.
So to answer your question no, there isn't a default country wide vox. Considering how cluttered the text channel gets it's probably a good thing that there isn't. In theory there COULD be one if everyone all agreed to tune to channel 101 (or any other channel 100-199).