Neither the web interface's System -> Licensing tab nor the CLI "license request key generate" command seem to exist... so how does one do that on these boxes?
You contact your Adtran distributor, give them the serial number of your device, and pay for the license. About two weeks later you receive a box. Inside the box is an envelope. In the envelope is a piece of paper with the license key.
If you want it in one week instead of two you can pay extra for expedited shipping.
I heard about a fellow by the name of Sam Morse who was working on a means to send messages instantaneously over long distances, but until then the pony express is your only choice.
Implementation of RFC1149 would be another option that should be considered.