This idea from a Sony Ericsson patent application is to add a cleaning slider to the display and couple it to the opening mechanism of the phone itself, Unwired View reports.

When the phone is open, the slider just sits at the top of the screen, as and when you close your clamshell phone, the slider moves down the display wiping it clean as it goes.

We're not entirely sure (a) where the wiped up muck goes, and (b) not convinced it's a winning idea ... There's nothing wrong with a quick wipe against your sleeve, surely?