How can you tell when a contact is open on their heytell, to receive messages?
HeyTell for iPhone Frequently Asked Questions
there should be a checkmark (perhaps green) next to the name?
What is the difference between the Low, Medium, and High privacy settings?
Low: Anyone can find you as long as they look for you using the contact information you set for yourself.
High: Only people that you have invited, talked to directly, or otherwise friended can contact you.
Medium: You can talk to friends of friends (if a friend has Medium or Low privacy, and their friend also has Medium or Low privacy).