This is what info I could find... not clear if SMS is supported on Cloud Server or not.
Enabling sms on local server
To enable SMS notifications on Local Server you need to provide credentials for SMS gateway (currently Blynk server supports only 1 provider - Nexmo. You need to create file sms.properties within same folder where server.jar is.
And fill in the above properties with the credentials you'll get from Nexmo. (Account -> Settings -> API settings). You can also send SMS over email if your cell provider supports that. See discussion for more details.