This depends on the availability of a suitable API. Unfortunately, providers haven't decided on a common one yet. Sun were working on one (http://www.tbray.org/

This depends on the availability of a suitable API. Unfortunately, providers haven't decided on a common one yet. Sun were working on one (http://www.tbray.org/ongoing/When/200x/2009/03/16/Sun-Cloud http://www.tbray.org/ongoing/When/200x/2009/03/16/Sun-Cloud), although perhaps other providers will end up just cloning Amazon or Slicehost's. Check out Cloudkick (A YC company) for migration between Amazon and Slicehost.