The same thing that already happens when there’s a huge crowd of people in one spot - they overwhelm the cell towers and you can’t load anything on your phone. Not all that exciting.

There would definitely be a dramatic increase in car accidents.

Well, since cell phones use towers that define a coverage area "cell" and don't use satellites for comm, no satellites would be affected.

A satellite software crash

Consumer grade GPS/GNSS is unidirectional, so would completely unaffected. Cell towers will be overloaded but thats not a problem really. People would just stop using their phones again right away, because they cant go online.

Like what happens every 31 of December? Nothing actually, we're fine.

To see for yourself, ride any subway during rush hour.

So much scrolling.

You've never had a call drop or not connect?

That's what happens.