Samsung SCH-I770HAAVZW - Manual (Page 186)

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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 generate
less interference to hearing devices than phones that are not labeled. T4 is the
better/higher of the two ratings.
Hearing devices may also be rated. Your hearing device manufacturer or hearing
health professional may help you find this rating. Higher ratings mean that the
hearing device is relatively immune to interference noise. The hearing aid and
wireless phone rating values are then added together. A sum of 5 is considered
acceptable for normal use. A sum of 6 is considered for best use.
In the above example, if a hearing aid meets the M2 level rating and the wireless
phone meets the M3 level rating, the sum of the two values equal M5. This is
synonymous for T ratings. This should provide the hearing aid user with "normal
usage" while using their hearing aid with the particular wireless phone. "Normal
usage" in this context is defined as a signal quality that is acceptable for normal
operation.
The M mark is intended to be synonymous with the U mark. The T mark is intended
to be synonymous with the UT mark. The M and T marks are recommended by the
Alliance for Telecommunications Industries Solutions (ATIS). The U and UT marks are
referenced in Section 20.19 of the FCC Rules.
M3 + M2 = 5 T3 + T2 = 5