Connecting a serial console to the BT Fonera+ will get you access to the bootloader. Settings are: 9600 baud, 8N1. Once you’re in you can use fconfig to assign a network address to get back in later through Ethernet, no serial cable necessary. This opens the door to load 3rd party firmware such as OpenWRT.
Here I’m using a BusPirate to do all the dirty work.
Pinout: Rear of device facing left