The Federal Communications Commission (FCC) has passed a set of rules designed to make mobile phones more accessible to persons with disabilities. The FCC created a rating system to help consumers with hearing disabilities find a phone that will work with their hearing aids. Wireless phones rated "M3" or "M4" meet the FCC requirements for hearing aid compatibility and are likely to generate less interference with hearing aid devices. "M" refers to using the phone with a hearing aid in the microphone setting. The higher the "M" rating, the more likely it is you will be able to use the phone with your hearing aid on the microphone setting. Thus, M4 is the "better" or higher of the two ratings.
What is a "T" Rating? "T" refers to using the hearing aid set on telecoil. The higher the "T" number, the more likely you will receive better interoperability performance between your phone and hearing aid on the telecoil setting. Thus the T4 is the "better" or higher of the two ratings. Reduced feedback and reduced background noise are additional benefits of using a hearing aid set on telecoil during phone use. To determine the likelihood of successful cell phone use with your hearing aid, add the "T" rating number of the cell phone to the "T" rating number of your hearing aid.