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1. Tethering uses a lot of power and I'd have to plug my phone into a usb cord
2. Every time I would get into the car, I'd have to fiddle with my phone to set up tethering.
Like I said, it's easy and it only cost $10 a month.
Sorry, sometime early in the 7.0 versions Tesla put in a "feature" that disables wifi whenever the car is in drive. This means you can only use your phone's internet (via WiFi hotspot) while stationary.