In Exchange 2007 and Exchange 2010 if we wanted to see what devices people where using to check there email over active sync we would of used the following command.
Get-ActiveSyncDeviceStatistics -Mailbox "allen white" | fl
This command has been retired in Exchange 2013, if we want to see what mobile devices people use to check email on Exchange 2013 or Exchange 2016 then we use the following powershell.
Get-MobileDeviceStatistics -Mailbox "administrator" | fl
This command gives a LOT of information, from the users mobile phone number, the last time they connect the devices serial number, model number and much much more as seen below.
If we want to just pull out the important specifics of what device the user is connecting to Exchange 2013 and Exchange 2016 then we can use the following command.
Get-MobileDeviceStatistics -Mailbox "administrator" | Select-Object @{n="Mailbox";e={$mailbox}}, LastSuccessSync, Status, DeviceID, DeviceType, DeviceUserAgent, DeviceModel, DeviceIMEI, DeviceOS