Related:Google, on the other hand, have only been able to add the SMS feature in the Home users, since the landline phone calls were included, back in August. Now Alexa can send SMS to smartphones. As of now, this feature is limited to the US and will work on Android devices. Introducing the same feature for iOS platform wasn't possible due to the restrictions, placed by Apple, on messaging API for third parties. Whether this service would go international in future or not, is not yet clarified by the company yet. The procedure for enabling the Alexa SMS messaging feature is quite easy. After opening the Alexa app, the user has to go to the conversations tab and select the 'Contacts' options. Under that option, there is another option named 'My Profile'. The 'Send SMS' toggle can be enabled from here. Alexa was already empowered to send messages last year but that was not via SMS. This older feature would let messages, sent from one Alexa app user, be received by another Alexa app user only. But now, after the latest Amazon Alexa update, Alexa would ask you to choose between sending an SMS message or an Alexa SMS message.
Source: XDA Developers