MikeJ, if you are fully capable of speaking yet more comfortable with signing, then you do have that right. ADA doesn't only protect you if you're incapable. It outlines that if your preference is sign language, then that should be honored.
For a Deaf person who's more comfortable signing than voicing, this would imply being given an interpreter. For an oral Deaf person, this would imply being given CART services, captions, etc.
Services of their choice: if that means using sign language and not voice, then that's what must be given primary consideration. It's not too hard to find an interpreter in most areas so it's not an unreasonable request.
Whether written communication or lipreading and voicing is as effective as signing is up to the Deaf person. If a Deaf person doesn't feel as comfortable voicing and lipreading, then it's not equally effective.
The bit on interpreters:
Source
