Exchange Migration

First thought is..firewall.  Do you have your network firewall open to allow activesync.  Port 433 is the big one.  

Also did you install a client access server.  Get a certificate.  Does OWA work?

The reason I ruled out those is because email is working through outlook.  From outside my network the email comes through the firewall and hits sbs2003 still.  Then it forwards to my exchange 2010 server where my test mailbox resides.  Then shows up in my Outlook inbox as it should.  
When I use my mobile device, wouldn't I still hit the SBS2003 box using my SSL/DNS record of mail.whatever.com on port 443?

if the user has been migrated to the new server, then firewall, owa and activesync should all be based off the new server

Correct, when all is finished it will be but I'm trying to make it a little more seemless for the users.  Step by step I was wanting to just... get it up and working, then move mailboxes, then take down old server.

i just did a quick google search on your issue.  Lots of stuff to look at. but one caught my eye

By default members of an AD protected group like domain admins or enterprise admin cannot use microsoft activesync with a exchange 2010 server. They get a error like this: “Result: ActiveSync encountered a problem on the server. Support code: 0×85010014¿.