I used two different sites:
http://forums.macrumors.com/showthread.php?t=721946&highlight=tethering
For tethering
http://www.krillr.com/blog/3DPQHBZ3/i-have-tethering-and-mms-on-my-iphone-and-yes-im-on-att
(ensure you remove the .zip extension)
For MMS
All total took bout 10 mins
(I take no responsibility if this kills your phone)
Tested tethering over USB and Bluetooth, and had no problems sending MMS.