LG VX3400 User Manual page 74

Safety
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. The HAC
rating and measurement procedure are described in the
American National Standards Institute (ANSI) C63.19 standard.
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VX3400
For information about hearing aids and digital
wireless phones
FCC Hearing Aid Compatibility and Volume Control
http://www.fcc.gov/cgb/dro/hearing.html
Gallaudet University, RERC
http://tap.Gallaudet.edu/DigWireless.KS/DigWireless
.htm
Hearing Loss Association of America [HLAA]
http://www.hearingloss.org/learn/cellphonetech.asp
The Hearing Aid Compatibility FCC Order
http://hraunfoss.fcc.gov/edocs_public/attachmatch/
FCC-03-168A1.pdf