To sign by SMS, just follow the link you received by mail or SMS. You can open the link on a computer, smartphone or tablet.
Choose Sign now and enter your phone number, country code included and then choose Send code.
Example: The country code of Sweden is +46 so a phone number that is 070-8123456 should be written as +46708123456.
You will now receive a control code on your telephone. Put the code into the field on the webpage to complete the signature.