There are two main choices when you decide to buy home intercom systems. Those choices are between a wired intercom or a wireless home intercom system.
Really the only way you would decide to buy a wired system is if you already have an old one installed in your house, or you are building a new house. Otherwise the installation cost of running the wires would be too high.
If you are building a new house, you can simply have the home intercom systems run the wires for the system when they are doing the rest of the electrical and phone wiring. They can also do the final installation of the units after the drywall is installed.
If this is the route you want to go, you just need to give the electricians the installation manual for the system so they can see what kind of wire they need to run, and so they know what to quote you for final installation cost. There is nothing too complicated about installing modern home intercom systems so any electrician or even a telephone system installer should be able to do it.