Problems Adding Picklist to Calls Modular

Problems Adding Picklist to Calls Modular

I am trying to add a drop down or pick list custom field inside the calls module. Problem is that the option for adding a new section is not available inside the customization page. All other pages such as leads & contacts have the add new section available. Please help. Attached is a screen shot of the customization page and as you can see there is no section for add new section. Thanks