Q1. If I install Telegram app, will all my contacts (inside contact list, [contacts] button) automatically see I have Telegram installed? (I know if I installed whatsapp, all my contacts will know I have whatsapp, so I wonder if telegram is similar.)
Q2. I do not have person A phone number. Person A do not have my phone number. If person A has a telegram channel and I joined person A telegram channel, will person A know my number or will I know person A number?
Q3. How to prevent other Telegram users from knowing my phone number?
Q4. How do I know if a contact has Telegram?