Current cellphones are tested for hearing aid compatibility based on a FCC standard adopted in 2007 that doesn't account for interference with newer technologies, such as the 700MHz band used for 4G LTE by Verizon and AT&T. As a result, the FCC recently made a proposal for adopting the 2011 revision of the ANSI Standard, which uses a different method of measuring RF interference and has been expanded to include all bands from 698MHz to 6GHz, as opposed to the 2007 version, which only covered devices in the 800MHz to 950MHz and 1.6GHz to 2.5GHz spectrums.
The ANSI Standard has two sets of ratings: a "M" rating for acoustic coupling and a "T" rating for inductive coupling. Acoustic coupling uses a hearing aid's microphone to pick up the sound from inside the phone's speaker, while inductive coupling detects the signal from the speaker using a special loop inside the hearing aid called a telecoil.
The FCC hopes to adopt the 2011 ANSI Standard into the Commissioner's rules, after which there would be a transition period of one year before cellphones would need to follow the new requirements.