The below script will show ActiveSync details for users in an OU, this script also only reports devices that have synced after a specified date.

Add-PSSnapin Microsoft.Exchange.Management.PowerShell.Admin

Get-Mailbox -ResultSize:Unlimited -OrganizationalUnit domain.local/OU | ? {$_.Organizationalunit -eq "domain.local/OU "} | ForEach {Get-ActiveSyncDeviceStatistics -Mailbox:$_.Identity} | Where {$_.LastSuccessSync -gt '01/01/2014'} | ft -AutoSize Identity,DeviceType,DeviceID,DeviceModel,LastSuccessSync

by