Robin Good: iVisit 3D allows you to share and showcase your three-dimensional navigable panorama pictures on any iPhone or iPad.
"Developed for architects and designers, iVisit 3D allows users to view panorama renderings on the web."
On the App Store you can find both a free version
and a full professional one:
The professional version can read .pno files from Dropbox or other sources you provide and display it fully on your preferred Apple mobile device.
More info: http://www.ivisit3d.com