Replacing Telephone Cords - How Difficult Will This Be?

I've never done this, but I see a couple of options. If they are ducted, you might be able to run new wiring through the ducts. Another approach might be to remove ceiling light fixtures and/or speakers. This should give you access to any dead space between your roof and ceiling. You could then use a snake wire or other improvised tool to route the wires using the openings as access points. Depending on how things are configured it might not be too bad.