Samsung SPHM500 Service Manual page 244

The more immune your hearing aid device is, the less likely you are to
experience interference noise from your wireless phone. Hearing aid
devices should have ratings similar to phones. Ask your hearing healthcare
professional for the rating of your hearing aid. Add the rating of your
hearing aid and your phone to determine probable usability:
Any combined rating equal to or greater than six offers best use.
Any combined rating equal to five is considered normal use.
Any combined rating equal to four is considered usable.
Thus, if you pair an M3 hearing aid with an M3 phone, you will have a
combined rating of six for "best use." This is synonymous for T ratings.
It is suggested you experiment with multiple phones (even those not
labeled M3/T3 or M4/T4) while in the store to find the one that works best
with your hearing aid device.
To ensure that the Hearing Aid Compatibility rating for your phone is
maintained, secondary transmitters such as Bluetooth and WLAN
components must be disabled during a call. See "Turning Bluetooth On and
Off" on page 162 for instructions to disable these components.
220 Section 4A: Important Safety Information