Direct Routing allows users of Microsoft Teams to make calls through a telecoms provider such as V12, rather than Microsoft.
In the traditional model, customers would purchase, install and configure a Session Border Controller (SBC) from a Microsoft Certified partner. Once installed the SBC would then be connected to Microsoft Teams via SIP trunks and require maintenance and support throughout its life.
Choosing V12 as your supplier removes the need for any onsite SBC hardware as this functionality takes place in the cloud. The upshot is a simple, per user model with no ongoing maintenance or support requirements.