iOS and Android #OfficeInsiders, @ mentions are beginning to roll out in the latest #InsiderSlow updates for PowerPoint, Word, and Excel! Let your co-workers know you need their help or input, right from the document you are working on!

https://support.office.com/en-us/article/What-s-new-for-Office-Insiders-c152d1e2-96ff-4ce9-8c14-e74e13847a24?utm_source=t.co&utm_medium=referral#Platform=Android

Right now this feature is only for office insiders.