Please clarify your question: are you asking where the data is physically located or the product being utilized?
You refer to IBM, AMAZON, or EMC?
IBM has a cloud product and database lines. You would end up contracting not with IBM directly but with one of their channel vendors. The same goes for EMC. Amazon only has a cloud product. Here is the kicker - no cloud solution has been certified (yet) for HIPAA compliance security wise. Many vendors have product in the "cloud" but the data physically resides at a hardened facility and recalled via a web service.
Everything being equal. I wouldn't necessarily have issues with asking where the data is physically located because collocation data centers have ratings and are classified by the types of data they house. That being said I'm not sure the company would be so quick to offer that information up so that a lynch mob of phone callers would harass the vendor. Also - the facility would not disclose who their clients are anyway as a course of business.
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