code: public function contactAdd($phoneNumber, $firstName, $lastName)
      {
          $phoneNumber = $this->formatPhoneNumber($phoneNumber);
  
          return $this->exec('add_contact ' . $phoneNumber . ' ' . $this->escapeStringArgument($firstName)
              . ' ' . $this->escapeStringArgument($lastName));
      }
docs: Adds a user to the contact list
  
  @param int|string $phoneNumber The phone-number of the new contact, needs to be a telegram-user.
  Can start with or without '+'.
  @param string     $firstName   The first name of the new contact
  @param string     $lastName    The last name of the new contact
  
  @return string|boolean The new contact "$firstName $lastName"; false if somethings goes wrong
  
  @uses exec()
  @uses escapeStringArgument()