Developed by HLA-Wake County, Raleigh, NC
Telephones
nHearing Aid Compatible (HAC)
nCallerID
nVolume Control
nRinger Volume Control
nHigh Frequency Boost
nFlashing Lights
nJack (for ALDs)
nFM and Bluetooth
n
Technical Solutions
HAC effectiveness varies greatly on mainstream phone. 
Special phones exist for Hard of Hearing people for serious features.