People who have been using WhatsApp for a long time must have understood that a very common behavior of the application is the immediate interaction of it with the calendar of phone contacts. Until recently, you could only communicate with a new person in your life if their cell phone number was recorded on the calendar.
You can do it very easily these days – and the best without installing any additional application or navigation in settings.
Just type in a web browser the URL address wa.me/badbadbadbadx . Note: you must change all these "x" numbers by the number you want to contact, in this order: the country code (55, in the case of Brazil), the area code DDD (11, in the case of São Paulo) and the telephone number of the contact person. No additional signs, no spaces.