Accessibility for Deaf/Dumb

Morning All,

A client of ours has suggested putting some sign language images on 
their site that tells visitors to call a special phone line kitted out 
for braille based phones.

My gut feeling is that this is taking things too far and anybody that 
is deaf or dumb would be able to read normal text so the sign language 
would be unnecessary.

Am I wrong?

Any feedback would be appreciated.

Cheers,

Julian Voelcker
Cirencester, United Kingdom