You can verify a phone number is real and active without needing them to reply, or without someone even receiving a notification.
1) SMS supports receipt functionality, which means the sender can be notified when a message is delivered to a handset. This happens at the carrier level, so you can't turn it off.
2) SMS supports 'silent' messages which are a different message class that is not shown to users.
alt Hacker News
You can verify a phone number is real and active without needing them to reply, or without someone even receiving a notification.
1) SMS supports receipt functionality, which means the sender can be notified when a message is delivered to a handset. This happens at the carrier level, so you can't turn it off.
2) SMS supports 'silent' messages which are a different message class that is not shown to users.