What I'm NOT suggesting is that we fail to accommodate deaf users. We don't have a policy on how to accommodate deaf or sight impaired customers, but we rely heavily on non-phone based means of communication, like Skype, so I'd imagine we could accommodate deaf users relatively easily. We use well formed HTML with semantic markup, but could probably stand to do some testing with screen readers.
Come to think of it. This request has moved me to action. Staff resources are going to be updated with notes on accommodating users with disabilities, including links to TTY services in the resource handbook. Solving this problem is probably easier than you think. All the major phone carriers are required to provide TTY services [2].