After hours phone service - emergency call solutions?

[Ryan Murdock]

I am looking for a solution for after hours phone service for a small rental portfolio. I would like tenants to be able to call the "normal" business line after hours and leave a message. In the event of a real maintenance emergency I'd like them to be prompted for something along the lines of "Press 1 if this is an emergency" and have it ring forward to another number for an on-call maintenance person. 

Nothing has been set up yet so we're starting from scratch. The "normal" business line could be anything at this point - Google Voice or whatever would work for this kind of system.

We have a large maintenance company with a full blown multi-line phone system with tiered ring emergency capability which works great but is overkill for this particular situation and I need to create something completely independent of it.