One use case is the GSM network ran on Chaos Communication Congress hacker conference in Hamburg. They created an internal network for the attendees to - among other reasons - communicate for free:<p><a href="https:&#x2F;&#x2F;events.ccc.de&#x2F;congress&#x2F;2015&#x2F;wiki&#x2F;Static%3AGSM" rel="nofollow">https:&#x2F;&#x2F;events.ccc.de&#x2F;congress&#x2F;2015&#x2F;wiki&#x2F;Static%3AGSM</a>