Requirements

• Full-duplex
• Multi-party
• Mobile (DC powered for car or yacht)
• 100m range?

Extra requirements

• Free to talk
• Independent of mobile data connections

Physical and Data Link Layer

Bluetooth

• 100m range from an in-car transmitter is possible

SMesh

• no devices on the market?

802.11s

• 
  

Wifi

• mobile phone ~30m range is too short
• in-car basestation

Ideas

• Local wifi hotspot (range?)
• Mesh networking
• Android audio-conferencing app?
• TomTom integration?
• Teamspeak?