So I have exchange 2010 existing and a new 2013 exchange installed each in 2 different AD sites.  Mailflow works between the two, however I'm trying to see if theres a way I can keep users mobile access intact while I migrate users.  Right now if i migrate user to 2013 I lose that.  Is there a way I can configure to do some type of redirect so 2010 will forward OWA and AS etc to 2013 if the mailbox has been migrated?

You need to point all users to Exchange 2013 for ActiveSync (and other protocols) and let it proxy or redirect requests to Exchange 2010.

http://blogs.technet.com/b/exchange/archive/2014/03/12/client-connectivity-in-an-exchange-2013-coexistence-environment.aspx

The problem is external MX is pointing at the AD site that has the 2010, maybe I should create a subdomain for AS like mobile.domain.com and point it to the 2013 for the time being. Would that work?

Maybe for ActiveSync only.

yeah we don't really have alot on OWA, mostly all client or mobile,

You can have different URLs for the two versions but Autodiscover should point to Exch

autodiscover for internal you mean? so i should change the autodiscover.internaldomain.com to point to 2013

Hi,

Yes, you need to change the autodiscover.internaldomain.com to point to 201. In the existence environment, The Autodiscover service on Exchange 2013 can process Autodiscover requests for both Exchange 2010 and Exchange 2013 mailboxes.

Regards,

David