Casio G'zOne Commando User Manual page 302

What is Hearing Aid Compatibility?
The Federal Communications Commission has implemented rules and
a rating system designed to enable people who wear hearing aids to
more effectively use these wireless telecommunications devices. The
standard for compatibility of digital wireless phones with hearing aids
is set forth in American National Standard Institute (ANSI) standard
C63.19. There are two sets of ANSI standards with ratings from one to
four (four being the best rating): an "M" rating for reduced interference
making it easier to hear conversations on the phone when using the
hearing aid microphone, and a "T" rating that enables the phone to be
used with hearing aids operating in the telecoil mode thus reducing
unwanted background noise.
How will I know which wireless phones are Hearing
Aid Compatible?
The Hearing Aid Compatibility rating is displayed on the wireless
phone box.
A phone is considered Hearing Aid Compatible for acoustic coupling
(microphone mode) if it has an "M3" or "M4" rating. A digital wireless
phone is considered Hearing Aid Compatible for inductive coupling
(telecoil mode) if it has a "T3" or "T4" rating.
How will I know if my hearing aid will work with a
particular digital wireless phone?
You'll want to try a number of wireless phones so that you can decide
which works the best with your hearing aids.
You may also want to talk with your hearing aid professional about the
extent to which your hearing aids are immune to interference, if they
have wireless phone shielding, and whether your hearing aid has a
HAC rating.
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