Thank you for asking this question in the support community. What layer 2 protocol are you using to bond the T1s? Is it PPP or Frame Relay? Here is a similar post on this topic: https://supportforums.adtran.com/message/2292#2292
Also, here is the Configuring PPP in AOS guide and starting on page 6 is the multilink commands. I hope that makes sense, but please do not hesitate to reply to this post with any questions or additional information. I will be happy to help in any way I can.