If you allow access, your contacts are continuously synced with Telegram. Thanks to this, you can easily switch to Telegram without losing your existing social graph – and connect with friends across all your devices. We use data about your contacts to let you know when they join Telegram. We also use it to make sure that you see the names you have in your phone book instead of the screen names people choose for themselves. You can disable contact syncing or delete your stored contacts in Settings > Privacy & Security on Telegram's mobile apps.