Hi,
I would like to add some more info the Call Reminder email that get’s sent as an alert (found here: include/language/en_us.notify_template.html). I would need to to add the phonenumber of the contact i’m going to call. This would make it possible to dial direct from my mobilephone by clicking the phonenumber. I tried to add {CALL_TO}, but that value is empty in the email sent out 
Is there by the way a list of what variables that can be used in emails?
Anyone?
Probably (sorry but I haven’t tried), instead of the call reminder you could use a template that you create within SuiteCRM and a workflow that sends the email when certain conditions are met (for example: 1 day before the call).
In this way you wouldn’t have to customise any code.
Also, read this thread
https://suitecrm.com/forum/suitecrm-7-0-discussion/13251-meeting-confirmation-emails-location
you’ll see where in the code all the variables get loaded, so they become available to the template.