How long before you notice someone is gone? How long is it that you think before others will notice you're gone?

One member of my group last night was telling a story about her sister just passing away. She said the weird thing she noticed was that her phone suddenly stopped ringing. It seems that her sister called her something like 8 times a day. The silence, for her, was very striking, and she said she liked having that silence. She didn’t need anyone.

There are many different kinds of relationships we have: close family, extended family, friends, co-workers, flutherites, etc, etc. If someone from these (or any other) categories were to disappear, how long do you think it would take you to notice? Why that long? On the other hand, if you were to suddenly disappear, how long do you think it would take people from each (or some, or one) of these categories to notice? Why?