Earlier quoted context omitted.
Last year, it was roughly 2/3 outbound vs 1/3 inbound, based on total talk time in the 6.5 days it was set up. 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%)…
Did you restrict any of the expensive international destinations in the voip.ms control panel? I imagine you wouldn't get that many people who wanted to call really weird places and have a 2 hour conversation from the playa, but some very costly destinations in per minute rate do exist in the voip.ms rate table.
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.