When can you send a Telegram message via NisWire?

1. If you have the contact’s Telegram username
   Yes, you can always send a message.
2. If you only have the contact’s Telegram number. 
   You can send a message if,
   - they have a "username" set for their profile, 
   OR
   - their "Who can send me a message" is set to "Everyone",
   OR
   - their “Who can send me a message” is set to “My Contacts” and your Telegram number is in their contact list.
   
   

Please note, these are as per the privacy policies of Telegram.