Sorry, currently we do not support porting phone numbers to Dingtone.
Per the Terms of Service that you agreed to when you signed up your Dingtone account, phone numbers assigned to you are owned by Dingtone or its suppliers.
You do not have any rights to transfer the phone numbers or to use the phone numbers separate and apart from the Dingtone service. Dingtone only grants you a permission to access a Dingtone phone number even you pay certain amount of Dingtone credits when you get the number.