Today, during the Microsoft Worldwide Partner Conference 2009, Microsoft announced the business and partner model for the Windows Azure platform including service level agreements and support programs.
Windows Azure, SQL Azure and .NET Services will be commercially available at the Professional Developer Conference 2009.
Upon commercial availability Microsoft will offer Windows Azure through a consumption-based pricing model, allowing partners and customers to pay only for the services that they consume.
Bandwidth across all three services will be charged at $0.10 in / $0.15 out / GB.
More details here.