Settings | Layout
These options will allow the customization of each panel's size and location and what is displayed on each panel. There are multiple preconfigured layout options and an option for custom layout. Once the preferred layout has been selected, what is displayed on each panel can be configured. Each panel on the layout has a number assigned. These panel numbers can be selected for each of the options (Calls, Contact Search, etc.)
The same panel number can be selected for multiple options. In this scenario, tabs will appear for each option on the top of the panel.