Who called from 7037742121

Caller called at 3am. When voicemail picked up, They just hung up. 3am? What could be do important to call but not leave a message at that hour?

To them? FInding out if they can get any kind of answer at that hour. That serves well to pass along to other pests. If they know they can get an answer at all hours, they'll keep your phone ringing. If you can do without missing any emergency or important call, turn off the answering device, ringer or disconnect the line (pending landline).