I have internet long distance that charges for all outgoing calls. I also have a land line for local calls only. I designed this circuit to switch between land line and internet. The circuit also has a 3-way switch to turn the entire phone service off/on from two locations in my house.
Don't mind the artwork. The circuit is in there somewhere.
formatting link
One advantage is if my land line goes dead I can switch to internet phone and still make calls. I've been having a lot of that the past few months.