HATIS is one type of technology I have read about. It doesn't sound though like it's precisely what you are after.
I'd also try to contact a major wireless carrier, like Verizon, who would be more likely to generally cater to large groups of individuals with hearing loss (perhaps at the corporate level, etc.). IMHO contacting them via email may not be the best method to solve this problem unless you are initially inquiring about making an appointment to speak with a Verizon rep in person at a location near you who knows ESL, etc.
I also found the following site which might be worth contacting as well-
I am a full deaf person and right now the only phone I can understand at all on is a Virgin I don't even know much about it but someone got it for me very inexpensive which is good because I have to buy so much deaf equipment the costs are very high. Anyway it allows me to be able to hear it ring and would break a normal person's ear drum. The problem is it really doesn't have any equipment on it for the deaf and I still have a very hard time having a conversation and people get very irritated with me if I am in public because they can hear both sides of the conversation. I understand their not wanting to hear my conversation I don't even want them to but I don't have a choice.
Is there any company that actually has built in equipment so that I can use what we call a "loop" that makes it so only I hear the conversation also where it has closed caption maybe but most of all technology in it so that I can actually have a conversation with someone.
I appreciate any one who knows where for me to search what companies do put technology in their cell phones for the deaf.