Thanks, all working once I put the Fon+ and my home network on separate networks.
Both interfaces look like the following on my Mac when working:
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether c4:2c:03:0c:7f:d6
inet6 fe80::c62c:3ff:fe0c:7fd6%en0 prefixlen 64 scopeid 0x4
inet 10.110.0.1 netmask 0xffffff00 broadcast 10.110.0.255
inet 192.168.2.1 netmask 0xffffff00 broadcast 192.168.2.255
media: autoselect (100baseTX <full-duplex,flow-control>)
status: active
en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether d8:a2:5e:8e:80:a8
inet6 fe80::daa2:5eff:fe8e:80a8%en1 prefixlen 64 scopeid 0x5
inet 192.168.1.103 netmask 0xffffff00 broadcast 192.168.1.255
media: autoselect
status: active