Thanks for posting on our Support forum! Call waiting is enabled and disabled on the voice user associated with the FXS port in question. Below is an example.
voice user 1001
connect fxs 0/1
ADTRAN Technical Support
I went ahead and marked this post as "assumed answered". Feel free to mark any correct or helpful answers from this post. If you still need assistance with this issue I would be more than happy to help, just let me know in a reply.