Exchange 2003 & 2010 Coexistence Period (Change NameSpace)

Hello,

I have question on changing the namespace.

Currently my organisation is on Exchange 2003 and planning to move on to Exchange 2010. We use the external namespace is OWA.companyname.co.in and want it to change to mail.companyname.com when implementing exchange 2010. Is this possible??

If yes I can change the namespace when installing the 1st CAS, Do I need to rename the existing namespace on Exchange 2003 to legacy.company.co.in or it does not matter should I leave it as it is ???

My concern is simple I want to change the namespace from owa.companyname.co.in to mail.company.com. Please help me on my concern with your valuable inputs in the details.

Thanks

Prashant