Hi Chris,
This is a very delicate issue. This first thing I would do is go visit the client if at all possible. Try changing the handset (not all handsets will have the exact same accoustical properties) and check all the volume settings. See if he/she has had to turn up the volume on the hearing aid because of the lack of volume on the handset? Try different combinations of headset/hearing aid volumes to see if it makes any difference. Find out what they use at home and how that works for them. If necessary, we have ordered the same phone type as their home phone and installed it using an analog VG port. I would also order the Walker amplifier to give them a far greater volume adjustment range to try and find a satisfactory level. There is no easy answer in these situations, but if the user knows you are trying it goes a long ways.
Cisco has made every effort to meet disability requirements, but as with everything in life there are no "one size fits all" solutions. Have a look at the following compliance docs;
The handset is Hearing Aid Compatible (HAC) and meets FCC loudness requirements for Americans with Disabilities Act (ADA). Section 508 loudness requirements can be achieved using industry standard inline handset amplifiers such as Walker Equipment W-10 or CE-100 amplifiers.
From this 7940 doc;
http://www.cisco.com/en/US/products/hw/phones/ps379/products_data_sheet09186a008008884a.html
Hearing Aid Compatibility for Cisco Wired IP Phones
http://www.cisco.com/en/US/products/hw/phones/ps379/prod_bulletin0900aecd8025f09b.html
Hope this helps!
Rob
