The Windows Azure Management Portal now enable you moving your SQL Azure servers between different subscriptions, informs Microsoft "To move SQL Azure servers between subscriptions you need to be an account administrator, service administrator or a co-Administrator for both the source and target subscriptions."
"For example, customers can now move their SQL Azure servers and databases in that server from a trial or introductory subscription to a different subscription that hosts their production services and resources," Microsoft explains.
Note: "Moving a SQL Azure server doesn't involve a physical move of your SQL Azure server or databases (remember that a SQL Azure "server" is always a logical server which contains your databases that have multiple replicas for high availability). The move only changes the association of the SQL Azure server from one subscription to another." Microsoft said.
Please be aware; of the "impact to your bill as different subscriptions may be billed based on different offers that they are associated with," said Microsoft.
How to Use the Move Server Feature?
Once you login to Azure Management Portal, navigate to "Database" section, you'll see a new "Move Server" button in the Server Information pane, where you'll see various subscriptions for which you're a service administrator in the top left pane where the subscriptions, SQL Azure servers and the databases are listed.
Clicking on the button brings up a dialog that has a drop down selector which enables you to select the target subscription from all of your available, active subscriptions for which you are a service administrator. Select the subscription that you want the server moved to and click "OK".
In a few seconds the portal will refresh and you'll see SQL Azure server you moved now listed under the target subscription. Where subscription "Azure Sandbox2 User 0389" has the SQL Azure server and the database that was moved.
Please refer to the MSDN documentation to understand more about subscription management in Windows Azure.