You can put a button in your email message that acts like a clickable link to activate web pages, email addresses or phone calls.  This works only from emails or templates you created at Preferences> Communication Builder.
Add your button
  1. Click the name of your email message to open it.
  2. Click and drag the Button element to the desired position.
  3. Double-click to add text to your button.
  4. In the Button panel to the right of the message you can choose color, font, alignment, etc
Make your button a link In the Style section of the Button panel.
Web page link
– Link Type: Web
– Protocol: http://
– URL: paste the web page address
Email link
– Link type: email
– Email: email address
– (optional) default Subject and Message
Link to call a number (must be reading message from a mobile phone)
– Link Type: Web
– Protocol: Other
– URL: Type the phone number in this exact format tel:+000 000 0000
Save your message! 
Test your message – click the name of the message to re-open it and test from the bottom of the screen.