Use your Braintower SMS Gateway to send notifications of the Check_MK monitoring system.
Firstly activate the Notification Plugin for the Braintower SMS Gateway
cp share/doc/check_mk/treasures/notifications/braintower local/share/check_mk/notifications/
Enter a system user, his password and the URL for the HTTP API in the Notification Plugin
username = "apiuser" password = "secret" location = "http://192.168.1.1/api.php"
If you now create or edit a Notification Rule, you can use your SMS Gateway as Notification Method to send notifications by text message.