I agree with allowing deaf to at least have an access to TTY. It's almost like denying a wheelchair to a disabled person in prison and expect them to walk without it if they want to move around. It's really not fair that prisoners who can hear can use the phone and deaf people can not. People can't help it that they are deaf (or can't walk or blind)
TTY is kind of being phased out. Video phones, captel, SMS, etc.. is becoming the standard.