wow, I had no idea, I thought everyone could here everyone if they were in range and on the correct channel..
That is a bad limitation.. sometimes it is very awkward to type your callouts.
It isn't one that really can be helped, unfortunately.
Each voice server has its own UNICOM frequency.. but for any sort of voice UNICOM to work, everyone would need to be on the same voice server. And with that, consider the uncontrolled airport; if they had the same UNICOM frequency, everyone would be hearing callouts for pilots at airports that have no bearing on what they are doing.
For example.. say you're in the pattern at some out of the way airport, like KPQI (Presque Isle, Maine), and I'm on final at another out of the way airport, like KDUG (Douglas-Bisbee Int'l, Arizona). You're making calls to UNICOM about your intentions; I hear them. Does your callout mean anything to me at my airport, some 2500nm away?
Then think of pilots in Europe, Asia, or Australia, as this could happen on any voice server.. Someone on final at EHAM (Amsterdam Schiphol) hearing someone on final at GVAC (Cape Verde Islands). Neither callout matters to the pilots here, as they are no-where near eachother.
Also, range comes into play. If your airport has the same UNICOM frequency as another airport clear across the country, you'll hear those, too. So there are a fair number of limitations to overcome for voice UNICOM, on top of that XSquawkbox, and Squawkbox don't have or use it; and since we can't control what the pilot uses to connect to the network, the main medium that all pilot clients can use is text.
BL.