If you can convince them to trench or directional bore, that would be the best. However, it will be a lot of money. Anything radio is not guaranteed. However, I understand that universities are having success with a wireless mesh... Companies like firetide provide this. Also, do not put in VIKING... that is an intercom.. You are looking for a solution such as:
Talkaphone
Gaitronics
Codeblue
Zenitel
Command
Hope this helps.