Well, that's disappointing. About a year ago, I came within inches of purchasing service with Phone Power.* At that time, they claimed they were just finalizing the details on how they'd make their service available to SIP credential needing mobile devices like the Internet Tablets.
Unfortunately, we do not share SIP Credentials. We can support IP Phones, but only those listed at our web page, copy / paste the following URL to your browser and press enter: to view the BYOD Devices that we support http://www.phonepower.com/services/voip/byod.aspx