Here's the link to the article I found first:
http://money.cnn.com/2016/11/18/technology/amazon-echo-att-texts/index.html?iid=ob_homepage_tech_pool
And here is the link to AT&T's site with instructions on enabling the skill and setting up your contacts.
https://www.att.com/offers/send-messages-amazon-echo.html?partner=LinkShare&siteId=TnL5HPStwNw-LTUL5e6S_fk8WdcjaA6x3w
http://money.cnn.com/2016/11/18/technology/amazon-echo-att-texts/index.html?iid=ob_homepage_tech_pool
And here is the link to AT&T's site with instructions on enabling the skill and setting up your contacts.
https://www.att.com/offers/send-messages-amazon-echo.html?partner=LinkShare&siteId=TnL5HPStwNw-LTUL5e6S_fk8WdcjaA6x3w