Well, after recompiling the source of tjtag 3.01 with the addition of
{ 0x017E, 0x1301, size8MB, CMD_TYPE_AMD, "Spansion S29GL064M U (8MB)" ,128,size64K, 0,0, 0,0, 0,0 },
supplied by Jal2, allowing support of the uniform sector 8mb flash chip S29GL064M90TAIR7, using the laborious efforts of beyondwind's pinout hunting, I was successfully able to not only revive my bricked ip8100, but change the default envars of the original firmware, effectively allowing the permanent alteration of the default admin password, the original provisioning hash dir and crypt key!
I can't begin to thank you both for your help. There is no way I could have done it without you!
...to reiterate for any others poor bastards playing with these ti-ar7 devices

(every doc I have read mentions the below bootloader addy as universal between them)
PSPBoot Name Start End Size
BOOTLOADER 0x90000000 0x90010000 0x010000 (64K)
boot_env 0x90010000 0x90020000 0x010000 (64K)
tjtag -backup:custom /window:90000000 /start:90000000 /length:20000 /nodma /silent
Edit Envars with a good text editor to remove bs vonage defaults
CONSOLE_STATE unlocked
ADMIN_PWD ABW9wzpK6VV4Q (Admin)
CRYPT_KEY "change" (must be in hex and divisible by 2)
HASH_DIR "change"
Save and flash
tjtag -flash:custom /window:90000000 /start:90000000 /length:20000 /nodma /silent
make sure you use a pre 2007 firmware because the web interfaces for voip settings are broken intentionally (you may downgrade via tftp in the manner described below concerning reflashing old firmware)
finally, wipe out the config partitions for a & b (ip8100) or the cyt private partition rtp300, moto vt2x42, pap2v2,wrtp54g) so defaults are custom or blank respectively (-refer to the oldwiki for exact addy space)
ip8100
CONFIG_A 0x90400000,0x90420000
CONFIG_B 0x90420000,0x90440000
tjtag -erase:custom /window:90000000 /start:90400000 /length:40000 /nodma /silent
Upon entering the web interface, under the provisioning tab enter http://127.0.0.1 as both the provisioning and firmware server to prevent provisioning errors, then fill in your details for the given service. Your device will only accept [abcd] + [0-9] as the auth user name per the closed ggsip app sadly, but any combination of those characters works at any practical length, though I am not sure the limit.
Openwrt via serial @3.3v 115200,n,8,1,hw
To install openwrt from pspboot so to yield access to all flash memory, create a new partition encompassing all of the memory following the bootenv addy, format it, set it active, and tftp your image. Connect your ethernet cable to wan (as you will not need to switch it later) using a static ip on the box with your tftp server, making sure first to set the router's ip to the same subnet so it can talk. Your vars may be already good, or different depending on whether you have adam2 or an earlier pspboot, so make sure first; at the pspboot prompt "printenv" will show you what you are working with. In addition "printenv envlist" will give you some alternate envs which have yet to be set.
setenv SUBNET_MASK 255.255.255.0
setenv FULL 0x90020000,replace-with-end-addy-refer-to-openwrt-wiki
setenv BOOTCFG m:f:"FULL"
tftp -i your-tftp-server-ip your-image FULL
Only wan works, but it is good enough for you to run an openvpn server and icecast 
Since your bootvars will be maintained, flashing the old firmware is as simple as resetting one of the original partitions as active after formatting and tftping the original fw from the pspboot serial console.
e.g.
tftp -i your-tftp-server-ip your-firmware IMAGE_A
setenv BOOTCFG m:f:"IMAGE_A"
refer to if in doubt or in trouble:
http://tinyurl.com/yhsaqmf oldwiki
http://tinyurl.com/yg8d8oy
http://tinyurl.com/yb5w5p8 pspboot guide
Thanks again guys!
(Last edited by yopo on 10 Apr 2010, 18:54)