This support notwithstanding, it is our opinion that the work being done by the Open Stack interest group -- supported by Dell, Rackspace, NASA, Citrix, Cisco, Canonical and over 50 other organizations -- will deliver the most useable interface code the soonest, offering a de facto standard that is likely to precede ISO standard adoption by years. The code can be obtained under the Apache 2.0 open source license. (Information on the organization can be found here).
Short of widespread adoption of a standard set of interfaces, cloud storage users have access to a number of virtual and physical appliances to connect their existing systems using block storage or file storage interfaces. These provide several advantages.
First, the appliance provides an interface to cloud storage as if it is any block or file storage system. Second, an appliance that provides a transparent interface to a number of cloud service providers is an insurance policy against either technical or contractual difficulties with a service provider. This has been referred to as the Hotel California syndrome - you can check out but you can never leave.
Finally, these appliances offer WAN acceleration features like compression and network flow optimizations that address the bandwidth cost issue.
With increased pressure to provide more storage at lower or similar capital and operating expenses, the catalyst to adopt a public cloud strategy will continue to increase adoption across organizations of all sizes.