You can build a conference call line with Twilio Studio without writing any code. To start, create a new flow in the Studio Dashboard and select "start from scratch." Add a "Say/Play" widget to provide a message to callers before connecting them to the conference. Then add a "Connect Call To" widget to connect participants to the conference. Finally, configure your Twilio phone number to use the studio flow by selecting the correct options in the Phone Numbers dashboard. With these steps, you can create a fully functional conference call line using Twilio Studio.