Calls go straight to voicemail after one ring or not at all
Text messages stay as green bubbles and never show delivery status
iMessage texts do not show “Delivered” or “Read”
FaceTime calls do not connect
You cannot see the person’s profile picture or status updates in some apps
You are unable to contact them through normal phone calls or messages
Messages may still appear to send from your phone, but never get a response
Try calling from another number and see if it goes through
Try contacting them through another app or account to compare behavior