None of Apple's accessibility features impede the use of FaceTime on the iPhone, as of 2015. FaceTime is a useful tool for those using Apple's accessibility features, since video calls are perfect for communicating through sign language and lip-reading.
The user can also add personalized vibration alerts for incoming FaceTime calls. These features make FaceTime particularly good for the deaf and hard-of-hearing community.
Switch mode allows users with motor disabilities to use an external switch in conjunction with the FaceTime camera to highlight and select objects on the iPhone screen. Further, Siri can open FaceTime and make calls to iPhone contacts if a person is vision is impaired or has limited motor functions.