My Media is only available on the Slingbox 500. If you are interested in more information, this link will give you more details about the feature.
Product Manager @ Slingbox
The 'My Media' feature was going around on the tech sites that it was avaliable to owners of the 500 now and was eventually going to be implemented into the 350 in a future upgrade. See here for the info from engadget. Whether this was correct or not it was being quoted by numerous sources.
"An update to the Slingbox 500 at first, and the 350 later this year, adds a local My Media sync component that lets Android or iOS users offload photos or videos to a USB drive attached to the Slingbox -- they just have to stream their content instead of chewing up their mobile device storage."