Calls are made/answered on one telephone line just like with any other phone. At the same time, captions are provided over a second telephone line that automatically connects to the Captioning Service. This lets you turn captions on/off on Line 2 at any time in the call without affecting the voice conversation on Line 1. It also lets people call your phone number directly (on Line 1), and you will get captions of the call (over Line 2).