The Model 3 does not come with HomeLink built-in anymore. It can be purchased as an accessory after the fact for $300.
My suspicion is that this was done to keep licensing costs to HomeLink by Tesla low, so that instead of it being licensed on every car, it is just on the ones that need it. Annoying for those that need it, but good business strategy. On the flip side I like that the Model 3 doesn't come with XM radio, which is a waste on most cars.
A service center receives the accessory when ordered and then a mobile tech can come and install it if you do not want to go to a service center.
My local mobile tech came over with the part and installed in my garage. The install requires, both hardware and software to be installed. The hardware gets installed behind the front bumper, which must be removed by the tech and then the software loaded remotely and finally the user configuration.
The configuration is simple. Just click on the HomeLink icon and configure attach to the existing garage door as per the instruction here: https://www.tesla.com/support/homelink-faq
|Configuring HomeLink on the Model 3|
Awesome video at the end of this blog.