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.