AT&T, much like the other wireless carriers in the US, are looking for ways to continue adding subscribers. Which is becoming tough, now that the smartphone industry is a bit flat and there's not much growth going on these days. AT&T has been partnering up with many car makers to help bring in more customers but also bring their network everywhere. AT&T has actually been in partnership with Audi since 2014, Audi is also owned by VW Group along with Porsche.
In Barcelona today, the two companies announced a multi-year deal with Porsche, and AT&T will be bringing their 4G LTE network to some 2017 models in the US. At this point, neither company has announced which models in particular will be getting 4G LTE support. Although we should know in the next few months as 2017 models begin to be announced and debut at auto shows including the upcoming shows in Chicago and New York.
Along with this announcement, Ericsson announced that they would work with Geely Automobile Holdings of China to develop "an industry-leading connected car platform". This is going to be important for AT&T and other carriers as they look to get into automobiles in the near future. Ericsson is responsible for the majority of the hardware found on towers here in the US (and other countries). Hardware that we use everyday to send that tweet, or that Snapchat on our smartphone or tablet.
Currently, AT&T is the only US carrier to announce any type of partnership with an auto-maker, although it's likely that could change in the near future. All cars from GM, Audi, Volkswagen and a few others, come with a trial of AT&T's 4G LTE service in their vehicles (hence why you see AT&T adding around a million connected cars each quarter). After that trial is up, customers can decide to keep it, or not. Users that already subscribe to AT&T, can add their car to their account for $10/month. Which will then use data from your pool of data that is shared with the other devices on your account. So if you have a 10GB plan with two smartphones and a car, that 10GB is accessible to all three products.