The AR11 is a rare a reference design device, manufactured by Compal Communications built on the Texas Instruments' Perseus chipset. It was a key device in the development of the Microsoft Stinger operating system. The AR11 was used by the Microsoft team as an internal prototype around the same time as the Avenger prototype phone and was known by at least three different names: AR11, Avenger2, and Red-E. There were several firsts on this device including a magnesium mechanical design which was unique at the time, the ability to debug via an Ethernet-capable connector, and support for charging and sync via a mini-USB connection. It was extremely robust, and performed extremely well in drop tests thanks to its ground-breaking magnesium ME design. To support developers, the Microsoft marketing team created a special kit which included an AR11 phone and other collateral for 3rd party software developers to create Windows Smartphone apps. Prototype builds and manufacturing were led Compal Communication's Osman Wang and his team at Compal Communications -.

The Microsoft engineering design team working on the AR11 comprised of Matt Taylor, Kabir Siddiqui, Jeremy Jacobson, and Dave Voth. You may have noticed that the model in the Mobile Phone Museum collection has some unusual damage to the back of the device. This was the result of the dog owned by the donor, Mike Yonker, inadvertently getting hold of the phone and using it as a toy!