It would be great if this feature could be used without having to first set the Calling Number ID via the web. For example, if a user had 2 additional numbers previously verified, dialing a prefix would allow you to place the call and deliver a different Calling Number ID on a per call basis.

For advanced/BYOD users this could be done fairly easily, and is similar to using a PAYG providers for outbound calling.

Of course, I'd expect with both Voipo-provisioned devices or BYOD, there's a considerable development and configuration management effort required by Voipo to make this happen.