Looks like the Cortana team is putting the final touches on their Uber integration. Starting today some users, including ourselves, noticed that under Cortana's Notebook > Connected Accounts an option for the call-up car service has appeared. The ability appears only to be for those using Insider releases of Windows 10 and not build 10240.
Unfortunately, once you begin the process of linking Cortana to Uber, it appears to fail. This issue is likely due to something on Uber's end as the coordinated effort goes forward.
Full story from the WindowsCentral blog...