LG G Vista - Manual (Page 209)

207 Safety
The wireless telephone industry has developed a rating system for wireless
phones, to assist hearing device users to 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
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 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’s acceptable for normal
operation.