Line is the worse violator of these principles. Last I used it, in order to install it on another device, you had to back up all that device's data (contacts, etc) to a computer, put your account on another device which then triggers a non negotiable wipe of the other device's data whenever it connects to the internet, then download the backup to your new device. Hell.
The first of the two bad thing about Line is that connection to a phone number. Wife got a new iPad, and, because of the other bad thing - that Line only works on a single device - it had to be 'moved' to the new iPad. Which needs a confirmation by phone message. And that phone was in Japan, unlike my wife, and wouldn't have worked for text messages even if she had brought it (phone plan didn't allow international calls or text). Contacted Line and got all kinds of useless advice - at least there are people in the other end - but nothing worked.
Had to create a new account.
The backing-up and restore is the easy part. Not much help if you can't move the account due to that silly phone number lock-in.
All these problems would be solved if they allowed us to use Google voice number. It is a number that's attached to my email and one that I won't discard (assuming I would lose it due to in activity). But no. Even Uber doesn't allow me to use a Google voice number.
