INET Framework developers and contributors discuss matters in the inetframework-contrib Google Group.
If you are interested in INET more than just doing a quick simulation with it, we definitely recommend you to sign up. Google Groups has the advantage that it can function both as a mailing list and as an online forum.
Important: When signing up, please write one or two sentences about your motivation, otherwise your subscription will be refused. We are doing this minimal filtering of applicants to keep the discussion forum useful.