The setup: Detective's office phone gets broken, so she goes out to get a new one. The one she gets will ring randomly sometimes, and she can hear events that she should not be able to hear, i.e,
The chaos on the bridge of the Titanic, just when they've discovered they're about to hit the iceberg
The final moments of MH370
The murder of her partner in the police force, which hasn't happened yet
A conversation in Hell itself, where two demons discuss a plot to overthrow Satan (full disclosure, not sure if I'll use this last one, but I thought I'd jot down anyway)
What reason could demonic entities have for doing this in general? I thought of just "For fun" but that seems like a cop out. I've generally written demonic things as after some concrete goal, such as a person's soul, death to increase despair, etc...