Is the phone more used for inbound or outbound? Calling the phone seems fun, but I wouldn't want to get in the way of a bunch of people standing in line to make a call, or use it for emergencies.
There were 1,460 outbound calls successfully made to 835 different numbers in 23 countries, with a total talk time of 34.8 hours. (This is down about 40% from peak years ago, now that there's more cell service and Internet available at Burning Man.)
There were also 5,658 inbound call attempts, and 676 (12%) were answered with a total talk time of 17.2 hours. 4,070 incoming calls got a busy signal and 912 got no answer.
And you can't make an emergency call on it (which is written in all caps on it); flagging down someone with a radio is the right way to get emergency services out there.
And there are occasionally people who have trouble with the concept of "free 5 minute call" (that it hangs up after) not meaning "just keep dialing back for an hour or two", even with a long line behind them. I can't ban specific outgoing numbers with voip.ms, but once I ended up just disabling all calls to the country that a problematic user kept coming back and repeatedly redialing.