I love Tesla and have nothing but respect for the people who work there.
That said, I hate your service center telephone policy with the fire of a thousand burning suns.
Why would you force me to choose between showing up uninvited and making a reservation with my thumbs? At least let me make the appointment at tesla.com using my computer.
Even then, this type of asynchronous communication sets everyone up for aggravation and failure. It would seem you already know this, because you don't shackle your salespeople to this ill-conceived approach. Efficient communication often requires a series of dependent questions and answers that are not even remotely suited to an app on a phone.
As a former employee, a customer, and current investor, I implore you to reconsider.