Exchange Server 2003 to 2010 Migration from Child to Parent Domain

Hi All,

I have five child domains  and one parent domain. Child domains has exchange server 2003 environement with differnet smtp namespace and email address polices based on the domains.

Now, We are planning to implement Exchange 2010 servers in parent domain and migrate the exchange server 2003 users from child domains to parent domain.

Could you please let me know best practice approach to do the migration and share the technical challenges and potential issues related to exchange and AD if you have.

Regards

M