It seems the idea of installing a hotel style of phone in the holiday cottage is a hit with our guests. When we greet them on arrival we mention they only have to pick up the handset and dial 10 to reach us free of charge.
The guests make good use of the facility, but don't abuse it.
So far no guest has asked for the outgoing call facility, preferring to use their own mobile phones. They'd find our call charges are lower than BT or their mobile providers (outside of plan), particularly for international calls.