Mobile operators face an increasingly competitive and demanding business environment in which technology is changing more rapidly than ever, which makes it imperative to implement future proof, end-to-end open network solutions to innovate and compete. The Software Defined Mobile Network (SDMN) solution is a multi-vendor, software-based end-to-end 4G/5G mobile network that includes an Open Radio Access Network (Open RAN), transport and mobile core solutions -- each virtualized and residing on commercial off-the-shelf (COTS) hardware. This briefing -- available for both the Option 2 and Option 7-2x Split RAN architectures-- provides a blueprint for a disaggregated, virtualized, best-of-breed, and fully open 4G/5G mobile network.