I have a 2017 C-Max Energi SE, and received the letter back in October or November. I went to my usual dealer, they had no idea what I was talking about, and said I could just download the 4G upgrade. ? After a few more dead ends, I found a dealer who could order it (they charged me ~$515). In January, I dropped off the car to get it installed, and I got a call the next day that they were having an issue with the install on another C-Max, and they were waiting for a response from Ford before working on mine. That response never came, so I took my car back until they get it figured out.