1.
mount a serial adapter to the fonera device
(the serial adapter documentation can be found at http://wiki.openwrt.org/OpenWrtDocs/Hardware/Fon/Fonera)

2.
set your terminal client to 9600-8-N-1 

3.
enter the RedBoot console by pressing CTRL+C

4.
copy root.fs and vmlinux.bin.l7 to your tftp server directory

5.
configure the RedBoot bootloader IP and TFTP server settings using
ip_address -l [local ip address] -h [remote server address]

6.
flash the unit by entering the following commands

RedBoot> fis init
About to initialize [format] FLASH image system - continue (y/n)? y
*** Initialize FLASH Image System
... Erase from 0xa83e0000-0xa83f0000: .
... Program from 0x80ff0000-0x81000000 at 0xa83e0000: .

load -r -v -b 0x80041000 root.fs
Using default protocol (TFTP)
Raw file loaded 0x80041000-0x802e3fff, assumed entry at 0x80041000
RedBoot> fis create -b 0x80041000 -f 0xA8030000 -l 0x002C0000 -e 0x00000000 rootfs
... Erase from 0xa8030000-0xa82f0000: ............................................
... Program from 0x80041000-0x80301000 at 0xa8030000: ............................................
... Erase from 0xa83e0000-0xa83f0000: .
... Program from 0x80ff0000-0x81000000 at 0xa83e0000: .

RedBoot> load -r -v -b 0x80041000 vmlinux.bin.l7
Using default protocol (TFTP)
Raw file loaded 0x80041000-0x80120fff, assumed entry at 0x80041000

RedBoot> fis create -r 0x80041000 -e 0x80041000 -l 0x000e0000 vmlinux.bin.l7
... Erase from 0xa82f0000-0xa83d0000: ..............
... Program from 0x80041000-0x80121000 at 0xa82f0000: ..............
... Erase from 0xa83e0000-0xa83f0000: .
... Program from 0x80ff0000-0x81000000 at 0xa83e0000: .

RedBoot> fis create -f 0xA83D0000 -l 0x00010000 -n nvram
... Erase from 0xa83e0000-0xa83f0000: .
... Program from 0x80ff0000-0x81000000 at 0xa83e0000: .

fconfig
enter the bootscript: 
fis load -l vmlinux.bin.l7
exec

save the config and do

reset