I recently Migrated from Exchange 2007 (with latest SP and RU) to Exchange 2013 SP1 RU6. Have done this migration several times with no problem. Everything is functional on the server - Mail flow, OWA, ActiveSync....
An interesting problem I have come across is that when selecting a Recipient Mailbox it does not show "Mobile Devices" under Phone and Voice Features for any mailbox. The users have mobile devices connected and they work fine.
If I run PS: Get-ActiveSyncDeviceStatistics -Mailbox #####
It shows the mobile devices associated with the mailbox.
I have checked the AD User Object to ensure inherit permissions is enabled on all.
On users that I know have a mobile device I have checked the attribute editor for the user and msExchMobileMailboxFlags is already set to 1.
Under EAC Mobile there are no custom settings. No Quarantined Devices. No mobile device mailbox policies set. The default is at that and not modified.
If I log into OWA as the user and select Options - Phone the mobile device is listed there.
The Exchange 2007 server has not been decommissioned yet. If I go into EMC and select a recipient mailbox it shows the "Managed mobile devices..." option even though it lists all mailboxes on the new server. As the old server is not the same ActiveSync version it does not allow me to list them here, but at least it shows them unlike the EAC.