1 Varies by brand and model, but usual a cellular connectivity module, aka telematics. Some cars you can simply pull a fuse, some make it hard

2 Killing the telematics by pulling a fuse can cut off inbuilt navigation functions or the entire display and control system depending on how integrated it is. Work arounds can include pulling the GSM module or faraday caging the antenna.

Need specific models for more specific answers.