Can't you just run in a length of greased cable in that?
So what do you do mate? Oh I'm a cable greaser...
They don't want cordless phones because it is unreliable but a wireless bridge is okay? IP is okay but VoIP is not? Getting some conflicting ideas here

The most reliable solution I guess would be to run VoIP over the existing data cabling but they don't want that. You can get fairly cheap FXO/FXS devices but finding one that is standalone and doesn't require a server somewhere might be more difficult.