DS 16B/30B modules can be upgraded to run either or. But it is all one, or the other. But i could have 2 modules, one running Avaya, one running Nortel.
Be wary of which "M" series sets you want to reuse, as not all of them will work.
See the docs here to help determine which phones can be reused...and which features are compatible.
it is from a few years ago, before IPO got park n page, and MADN....https://avaya.sharefile.com/d-s50dd2c21f3e422cb