You can get notifications as push notifications or email for free. However, if you prefer to be notified by SMS you can purchase SMS. To make purchases you need to be the owner of the farm. 

1. In the menu select "Manage Farm" and scroll down to premium features. 

2. Click on "Charge" which will redirect you to webshop.

3. Select the number of SMS you want to purchase and finalize the purchase.

4. Now you have SMS available for the farm.