The documentation specifies the interface as 10 / 100 but does not specify if the port is full duplex, half duplex or auto-sensing. How does the duplex setting work on this unit?

The MultiVOIP Ethernet port is auto-sensing. It will detect the capabilities of the switch port, etc. that it is connected to. SP, under Ethernet on the VOIPs front panel, will light to indicate a 100Mbps connection. MVP210/410/810/2400/2410/3010/210-G/410-G/810-G/210-AV
410-AV and 810-AV are also Auto sensing, but do not have the SP LED under Ethernet on current hardware levels.