How to use microphone based on windows mobile devices to communicate with each other in a intranet like a interphone communication? I do not have the thought yet.
You can use a Voice-over-IP application to communicate within your network. Just use Walky-Talky like apps like http://handheld.softpedia.com/get/System-Utilities/Communications/iTalkie-20330.shtml
If you are a experienced Windows Mobile C/C++ coder you may write such app yourself.