Hi @pike
Port 5060 UDP is SIP (VoIP). User Kristian seems to use his NethServer as firewall…
So it’s probably a port forward to FreePBX - at least the chances are high… 
Then again, maybe security by obscurity is the goal, and 5060 is only an obscure port for SSH, pretending to be a SIP port…
If you’re talking about real, steel tipped darts and not the plastic childrens game, you at least have the advantage and option of acustic feedback playing this variant…
My 2 cents
Andy