I can understand how important it is to engaging with your contacts! While you are correct alerts can help with this, I apologize at this time we are not designed to be a CRM. Have you tried setting up an automated series? Through there series you can schedule reminder emails to automatically send to your contacts. These emails can be include text letting them know you've tried to call them, or even text to remind them of an upcoming call. The date and time of these calls can even be inserted through custom fields under your contacts.