Hi HeatMan:

I installled an intercom made by Aiphone several years ago to go
between my house and workshop 150' away. It is a "professional grade"
unit and works quite well. They make units that support up to 10
stations, and have a variety of styles and options. They cost more
than the RS stuff, but are completely private, and in my opinion, look
and sound better.

NuTone is a common brand, but I have heard that they don't hold up
well.

Regards,
John.