Analog provides good quality signal for cochlear implants with no interference. Digital phones use various technology depending on the source. A cell phone with an audio output socket can drive a neckloop or provide direct output to the processor. Cell phones need some attenuation because they provide higher output levels that the microphone Flip phones may be superior. Use patch cords to separate the two systems.
Inductors are simple phone interfaces that are portable, low cost and handy in an emergency.
Adapters are not as portable but offer better quality. FM systems like those used in schools can create problems. The cochlear implant uses radio frequency just as these FM systems do, and this can create interference. For this reason it is important that personal FM systems be used only by cochlear implant recipients who can report on the quality of the sound they are receiving. Sound field FM systems reduce a lot of the technical issues because everyone can hear them.