There are many cell phone applications, including eVoice and Line2, that allow users to connect additional phone lines to their smartphones. To add another line, install one of the applications to your phone, and use the developer's instructions to connect another line. EVoice allows users to add other numbers to their phone, including toll-free numbers and numbers with different area codes. The application can also reroute calls to other numbers or send them directly to voicemail.
To add a second line to your house phone, contact the phone company, and ask them to add another line to your phone. Let the company know if you can personally make adjustments to the wiring inside the house, and ask when the company can send a phone technician to complete all the necessary work on their side. Once everything is ready for you to adjust the wiring, decide where you want to install the second line, locate the phone jack, remove the faceplate from the wall, and detach the red and green wires from the back of the jack. The black and yellow wires should remain connected.
Check if the line works by calling another number. If it works, wrap a piece of electrical tape around the green and red wires, and insert them back into the phone cable. Attach the faceplate back to the wall.