Re 2 - Blackberry Messenger used an eight character alphanumeric ID, and was enormously popular in the UK (not sure about other countries however) - until Blackberries died a death at the hands of Apple and Android...
BBM was different since the PIN was baked into the device so it as more seamless than even using your phone number.
The problem was when you change your device you can't migrate your PIN so I think it contributed to decline to usage as people moved to other BB devices or iOS/Android
This only strengths the argument why majority of chat apps use phone number as your username.
Was BB ever really mainstream? I know it had loyal following, particularly for business users. But, at its peak it had 80M users globally. Most people still had basic phones then, and many of those with BlackBerries probably had an IT department supporting them.
> Using BlackBerry handsets – the smartphone of choice for the majority (37%) of British teens, according to last week's Ofcom study – BBM allows users to send one-to-many messages to their network of contacts, who are connected by "BBM PINs". For many teens armed with a BlackBerry, BBM has replaced text messaging because it is free, instant and more part of a much larger community than regular SMS.
The problem was when you change your device you can't migrate your PIN so I think it contributed to decline to usage as people moved to other BB devices or iOS/Android
This only strengths the argument why majority of chat apps use phone number as your username.