Hi Nick,
The ellipsis brings up the Search for Customer screen, which allows you to search for a specific customer. I don't see where it says that you can create a new contact from that screen. This can be done however through customization. You could put a link in the customer grid on that search screen. That link could call up the CRM_Contacts screen which is used when you want to add a new contact. When entered, you can then select that new contact from the search screen and go about logging your call.
If you want to try this customization, I would recommend making a copy of the CRM_EditCustomer screen and taking a look at actions 6 and 7 for the Add Contacts button in the Contacts section. Those are the main actions you'll need. If you're new to customization, I'd go through our webinars on customization first.
Hope this helps.
- Adam