It's not just bad cellphone service, but sometimes server issues could have the same effect. Hyundai ran a car sharing service here in Amsterdam that used a combination of Bluetooth and cellular connectivity to remotely unlock cars and provision software keys for phones. Every once in a while, though, the app would crash and lose the software key, meaning that the car would end up back again on the map exactly where you picked it up without leaving you with a way to unlock the car. I am not sure what exactly was the issue as the app just errored out.

I'd have to call the customer service line, where they wouldn't know what to do as the car was already in use according to the backend. After a few times getting stuck, I came up with a solution which was to literally beg them to cancel the checkout so that the car was available again. They were trained to not do that as their information was that a car could not be left parked outside their service area, which was definitely not the case as I was able to start a new reservation and unlock the car. This happened quite a few times, so much so that I would already know the solution but had to spend an awful amount of time explaining it to the reps -- starting with uninstalling and reinstalling the app as told by them.

Then, some other company took over the system and started a new system with the same infrastructure and the app codebase. When it happened again a couple times, I was finally able to get hold of a systems programmer who debugged the issue with me while I was out in the wind. It hasn't recurred since.

Just wanted to share this story