Hello,
The 6900 phone loads are included with the Software Packs, but were not supported with earlier versions of the IOS. I believe the first version of IOS that supported the 6900 series phones was 15.1(2)T2). If you upgrade to software pack 8.1.0 or newer, the 6900 series phones should be included. The WIP310 phone is not a supported phone on the UC500 product line at this time.
Thank you,
Darren