Antivirus software is installed on all mobile devices
Mobile devices are typically entry points of infection for end-users. They should no longer be regarded as simple telephones but rather as a computer equivalent from a security point of view.
Mobile devices are becoming increasingly more popular points of access to networks. Their security is just as important as that of laptops and classic desktops, even if their operating systems gets attacked in different ways.
Also think about a Mobile Device Management tool to control (and update) the apps installed on a mobile phone, to prevent the proliferation of (malicious) apps and the risks they could pose to your company.