I had this, the quickest way I found was to export your contacts to your PC, then import your contacts to your new gmail account. As far as emails, you can forward all emails from one account to another within the settings of the domain account.
I decided to make the switch after having some issues with google checkout within the Android OS on a previous phone. I'm almost all set to completely get rid of my previous account 2 months later (without being aggressive on changing things over).