Even installing your phones close to the intercom stations does not completely solve the problem. At the same time, you'll hardly be reachable for intercom or call transfer. Most of the time, your existing phones will be sitting idle and your intercom stations as well, as usual in a household. That means waste of the money you invested in sophisticated phones and the expensive mural intercom system. With a cheap speaker-based wireless intercom system, you can't have a single piece of home automation equipment, those being incompatible with X10 technology.
Home automation is the basis for the most rewarding amenities in a home.
Never rule it out. Most people don't expect to have to alternatively push a button on your doorbox to talk, as they will have to if you put them in front of a cheap door box equipment. Not a conventional phone system. Not a conventional intercom system. See which Ultimatoll system best fits your application.