What is the voltage of a landline telephone?

Legality of making my own landline telephone?

• I want to make my own landline telephone powered by the Arduino. I read somewhere that there is a law here in the U.S. regarding devices attached to landlines. Would using an approved part scavenged from computer parts used to interface with the landlines allow me to legally connect my future homebrew telephone to the landline? Or do I not need to worry about any laws? Or are my hopes of using a telephone I created dashed upon the rocks below?

• Answer:

  You can build your own phone as long as the interface to the landline is certified in compliance with "Part 15" of the FCC rules, and perhaps Part 68. But that's not where the questions end... Just so you know, the phone line is considered "hazardous voltage" (48 volts) for the purpose of things like UL listing. If your device does not have a UL or other safety listed interface, anyone plugging it in will be operating at their own risk and their insurance company may not have to pay for any damage or injuries resulting from its use. You, on the other hand, will be sued for gross negligence, which often means triple the damages the jury awards to the plaintiffs.