I have done a lot of work with Aiphone with good results. Their video intercoms are one of the best out there, they only require two wires between master and door station units. I have also installed the multi master systems with several door stations. They are very easy to install and I have not really had any problems with them. Just keep ground faults off the communications wire. The only other ones I have used are Siedle, and stay away, far far away from them. The video units require somewhere around 20 conductors between master and door station and to top it off the instructions are only in German.
Jim
