Some mobile phones are measured for compatibility with hearing aids. If the box for your particular model has “Rated for Hearing Aids” printed on it, the following explanation applies.
When some mobile phones are used near some hearing devices (hearing aids and cochlear implants), users may detect a buzzing, humming, or whining noise. Some hearing devices are more immune than others to this interference noise, and phones also vary in the amount of interference they generate.
The wireless telephone industry has developed ratings for some of their mobile phones, to assist hearing device users in finding 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 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 be more usable with a hearing device’s telecoil (“T Switch” or “Telephone Switch”) than unrated phones. T4 is the better/higher of the two ratings. (Note that not all hearing devices have telecoils in them.)
Hearing devices may also be measured for immunity to this type of interference. Your hearing device manufacturer or hearing health professional may help you find results for your hearing device. The more immune your hearing aid is, the less likely you are to experience interference noise from mobile phones.