"Call me Button" a great little feature that transforms your button into a link to your phone number.
To use this, simply go to any one of your draft campaigns. Click on a button. In the right hand panel you will see the link input field. Add "tel:" and your number so it might look like this: "tel:+44597921458722". Click save and thats it! Now every time someone presses your button they will be prompted to make a call. This works well especially on a mobile phone.