Should TTY phone numbers be hyperlinked as normal numbers?

Question

Most site developers know to use the tel: syntax for phone number links to enable easy mobile dialing:

<a href="tel:555-867-5309">(555) 867-5309</a>

Should the same be done for TTY numbers? Are there other or additional techniques that should be used for accessibility?

Answer 1

According to the RFC3966 :

The terminal addressed can support any electronic communication service (ECS), including voice, data, and fax. The URI can refer to resources identified by a telephone number, including but not limited to originators or targets of a telephone call.

For accessibility, you should indicate within the content of the link that the phone line is a TTY.

<a href="tel:555-867-5309">TTY: (555) 867-5309</a>

Answer 2

Yes, it's enough (Maybe add some description that will say it's TTY number). A deaf person can click link in same way that non-deaf person can do so if you are not using sounds on your website it's sufficient.

Setting TTY on your phone: https://support.apple.com/en-ca/HT207033

If you plan making your site accessible for blind people too then I would suggest you reading https://webaim.org/techniques/hypertext/