You cannot use a digital multi-line telephone as a Hotline phone. A Hotline extention can ONLY be a single-line telephone connected to an 016 T/R, 008 OPT or 016 ETR (top 6 ports programmed as T/R ports) module. It should work as well on an older 012 Basic Telephone module.
Tom Daugirdas,
President
STCG, Inc.
stcg.com