Hearing aids have not previously always worked well with mobile phones, because of electronic interference between the 2 devices that caused static, whistling or squealing noises, or dropped words. New government regulations, together with significant advances in both phone and hearing aid technology, have made this incompatibility rare. To help consumers shop for the right hearing aid compatible cell phone, the new regulations include a standard rating system and labeling requirement.
Understanding the rating system requires a bit of knowledge about the modes that hearing aids can operate in. There is an M mode (which stands for microphone) and a T mode (which stands for telecoil). In M mode, your hearing aid uses its built-in microphone to pick up audible sounds from the environment and amplify them so that you can hear them. In T mode, the hearing aid uses telecoil technology instead. The hearing aid is able to pick up the electromagnetic signals from inside the phone directly. Currently, approximately 60% of hearing aids sold in the United States have a telecoil or T mode.
The rating system for these two modes of hearing aid operation uses a scale that ranges from the lowest sensitivity (1) to the highest sensitivity (4). To be labeled as hearing aid compatible (HAC) a cell phone must carry a minimum rating of M3 or T3.
In addition, many hearing aids (and cochlear implants) have a similar M and T rating to measure their sensitivity and their resistance to radio frequency interference. If you know the M and T ratings for your hearing aid, to determine its compatibility with any mobile phone, just add the two sets of ratings together. If you get a combined total of 6 or more, that is thought of as excellent, a combination of hearing aid and phone that will be highly usable. A combined rating of 5 is thought of as normal, and suitable for most people. If the combined rating is 4, this is thought of as acceptable but not very usable if you make a lot of extended phone calls.
Since being introduced, the new rating system has made it much easier to shop for a cell phone online and determine its compatibility with your hearing aid in advance. In the end, nothing beats a real world test so you may want to wear your hearing aid to the mobile phone shop and test out a few different phone in real conditions.