visually impaired:
GrIDsure have already been chatting with the RNIB and have had a positive response about the suitability of the system for the sight-impaired, see this response to the original GrIDsure article on the Reg:
http://www.theregister.co.uk/2007/10/04/pin_fraud/comments/#c_71369
and this:
http://www.gridsure.com/faq/show/411#q_614
The mobile application could be made to read out the numbers on the grid quite easily on most modern phones, which would still be protected from a "shoulder listener" by the GrIDsure system, in the same way as a "shoulder surfer" is defeated. (although that hasn't been built into the existing system)
Ben, from Masabi.