What do you think would happen if everybody who has a cellphone used them all at once...?
A satellite software crash...a mix in signals where you're getting on someone else's convo...what..?

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

So much scrolling.

There would definitely be a dramatic increase in car accidents.

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.

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.

And actual phone traffic is pretty low bandwidth, so if everyone called someone else at the same time, the dialing computers would be the weak link. Trying to establish all those connections at the same time.

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

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

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

That's what happens.