It'd be a wee problem if your phone runs of battery at the vital moment..
While those in London can use SMS to actually find a lavatory, folks passing through Western Finland will be required to bust out their handset in order to relieve themselves in select public restrooms. In an attempt to curb vandalism, the Finnish Road Administration has implemented a system along Highway 1 which requires restroom visitors to text "Open" (in Finnish, of course) in order to let themselves in. The idea is that folks will be less likely to lose their mind and graffiti up the place knowing that their mobile number is (at least temporarily) on file, but it remains to be seen if uprooters will simply take their defacing ways elsewhere or actually excrete in peace.
http://www.engadget.com/2008/02/05/finlands-roadside-toilets-now-accessible-only-by-sms/