How can I make a button link to an email?
You should use the mailto: link feature. Basically, you should put this to the button's link field:
mailto:test@example.com
This code will open the installed email application and fill the "to" field with the given email address. In the sample's case, this address is test@example.com
Set subject
You should put a?Subject=
after the email address like this:
mailto:someone@example.com?Subject=Hello%20again
This will make the email's subject "Hello Again"
Can I do the same with phone calls?
Sure. Use the tel: prefix instead.
Example:tel:+6494461709