The era of ICQ and Pokec
ICQ had numeric identifiers and statuses such as online, away and do not disturb. In Slovakia a huge phenomenon was the Pokec chat, where a whole generation wrote to strangers as well as to their friends from school.
Encryption
Modern messengers such as Signal and WhatsApp use end-to-end encryption. Only the sender and the recipient can read a message, not the service operator. The same applies to calls.
Beware of scams
Scammers pose as relatives (“Mum, my phone broke, this is my new number”) and ask for money. Always check by calling the original number.