Yes, Digium phones are hearing-aid compliant, for more information on about the phone specifications please check its datasheet.

What Makes a Phone Hearing Aid Compatible

Hearing aids operate in one of two modes – acoustic coupling or telecoil (inductive) coupling. Hearing aids operating in acoustic coupling mode receive and amplify all sounds surrounding the user; both desired sounds, such as a telephone's audio signal, as well as unwanted ambient noise. Hearing aids operating in telecoil coupling mode avoid unwanted ambient noise by turning off the microphone and receiving only signals from magnetic fields generated by telecoil- compatible telephones. 

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