def METHOD_NAME(url_root, username, id_string):
    """Returns SMSSync integration documentation."""
    urla = url_root + reverse(
        "sms_submission_api", kwargs={"username": username, "service": "smssync"}
    )
    urlb = url_root + reverse(
        "sms_submission_form_api",
        kwargs={"username": username, "id_string": id_string, "service": "smssync"},
    )
    doc = (
        "<p>"
        + _("%(service)s Instructions:")
        % {
            "service": '<a href="http://smssync.ushahidi.com/">'
            "Ushaidi's SMS Sync</a>"
        }
        + "</p><ol><li>"
        + _("Download the SMS Sync App on your phone serving as a gateway.")
        + "</li><li>"
        + _("Configure the app to point to one of the following URLs")
        + '<br /><span class="sms_autodoc_example">%(urla)s'
        + "<br />%(urlb)s</span><br />"
        + _("Optionnaly set a keyword to prevent non-formhub messages to be sent.")
        + "</li><li>"
        + _("In the preferences, tick the box to allow replies from the server.")
        + "</li></ol><p>"
        + _(
            "That's it. Now Send an SMS Formhub submission to the number "
            "of that phone. It will create a submission on Formhub."
        )
        + "</p>"
    ) % {"urla": urla, "urlb": urlb}
    return doc