Calling an Auto Attendant associated with an OCS dial plan for a non OCS enabled user goes directly to voice mail

I recently worked an issue where there were two dial plans defined in Exchange Unified Messaging, one for the Telephone (PBX) and the other for Office Communications Server (OCS).  When a call was made to the Auto Attendant associated with the PBX Dial Plan and dial by name feature was used for a non OCS enabled user, the call was routed to the users phone device and if the user failed to answer, the call was ultimately routed to voice mail.  If the user was enabled for OCS it failed to route the call.  This is expected behavior as the Gateway is unable to interpret a users SIP URI.  On the flipside, when a call was made to the Auto Attendant that was associated with the OCS Dial Plan and the dial by name feature was used for a OCS enabled user it would successfully route the call to the users phone device and if the user failed to answer, the call was ultimately routed to voice mail.  However, if the user was a non OCS enabled user the call would be directly routed to voice mail with option to call the users phone device.  The goal was to use a single Auto Attendant associated with a OCS Dial Plan as users were slowly migrated to Enterprise Voice.  Below is what we did to get it working.

Symptoms

When a call is placed to the Auto Attendant associated with a OCS Dial Plan from either an internal or external user and dial by name is used for users that are not OCS enabled but have E164 numbers defined in Active Directory, the call is routed to voice mail with no option to call the end user.

Cause

UM:
- Both the OCS Dial Plan and Auto Attendant were configured with a default setting of only allowing caller to contact users within the dial plan
- No defined Dial Rule Groups
- No defined Dial Restrictions associated with any Dial Rule Groups
OCS:
- No route defined to allow E164 dialing

Resolution

UM:
- Allow caller to contact Anyone in the default GAL
- Dial Rule Group created and defined to allow ALL
-  Allow ALL Dial Rule Group associated with Dial Restrictions
OCS:
- Created a route that allowed for E164 dialing