Toilet Models What Does The Sentence "some Toilet Paper Dispensers Can Double As IPod Docks" Mean?

What does the sentence "some toilet paper dispensers can double as iPod docks" mean? - toilet models

"Some business models toilet seats toilet, which you can download songs from an SD card, and some distributors of paper towels can double as an iPod-dock."

I do not understand, some distributors of paper towels doubling as an iPod dock. "Who can explain to me clearly.

Thank you very much for your help ;-)