Motorola AT Commands G24-L Developer's Manual page 431

Abbreviation
H
HCO
H Hearing Carry Over allows Speech Disabled callers who can hear well on the telephone to
listen directly to the person they are talking with. The Speech Disabled Relay user types
his or her part of the conversation on a TTY. A Communication Assistant (CA) then
speaks the typed conversation, word for word, to the standard telephone user.
April 15, 2008 G24-L AT Commands Reference Manual
Acronyms and Abbreviations
Full Name
Acr & Abbr-3