I am looking for an unbiased opinion . Customer needs up to 250 digital phones w/4 PRI's . 3-4 different companies sharing same PBX w/voice mail for all extensions. They prefer simple usage of features and the phone systems will require frequent changes with their DID/s . Which is a better system or better option ? Basically , if you guys had a choice which would you install the Panasonic 600 or the BCM 450? Thanks so much. Harry