I believe you do not need to have any active subscription or WiFi connection (to a hot spot like a phone our your home WiFi).Do you have to have an on-star subscription to receive updates.(OTA) Does it work, for example, with the communication of the data network from your telephone (LTE)
The first one I got was labeled 'infotainment'. The second one was not, so I assume it was a general 'system' updateI got two updates a week apart. The first one broke the Infotainment system so that even after turning off the car and opening the door, your iPhone/USB/radio kept playing until you shut all doors and locked the car with the keyfob. The second update fixed that. Each update took less than 10 minutes and were over-the-air (OTA).