Okay do you know you can run Get-CASMailbox -Filter {HasActiveSyncDevicePartnership -eq $true} to get a list of users that have an Activesync partnership.
Now if you combine this with Get-ActivesyncDeviceStatistics you can get more details too. Check it out:
Get-CASMailbox -Filter {HasActiveSyncDevicePartnership -eq $true} | foreach {Get-ActivesyncDeviceStatistics -mailbox $_.name}