Huawei M635 User Manual page 45

Some hearing devices are more immune than others to this
interference noise, and phones also vary in the amount of
interference they generate. The wireless telephone industry has
developed a rating system for wireless phones, to assist hearing
device users find phones that may be compatible with their hearing
devices. Not all phones have been rated. Phones that are rated have
the rating on their box or a label located on the box. The ratings are
not guarantees. Results will vary depending on the user's hearing
device and hearing loss. If your hearing device happens to be
vulnerable to interference, you may not be able to use a rated phone
successfully. Trying out the phone with your hearing device is the
best way to evaluate it for your personal needs.
M-Ratings: Phones rated M3 or M4 meet FCC requirements and are
likely to generate less interference to hearing devices than phones
that are not labeled. M4 is the better/higher of the two ratings.
T-Ratings: Phones rated T3 or T4 meet FCC requirements and are
likely to be more usable with a hearing device's telecoil ("T Switch"
or "Telephone Switch") than unrated phones. T4 is the better/higher
of the two ratings. (Note that not all hearing devices have telecoils
in them.) Hearing devices may also be measured. Your phone
meets the M4/T4 level rating. Hearing devices may also be rated.
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