A cliffhanger
To cliffhanger someone is to call them and say you have to tell them something important, then hang up before they can ask what it is.
'I have to tell you something!' Then she hung up. I threw my phone at the ceiling.
He said, 'I need to tell you something big!' Then he went offline. I cursed his name in 5 different languages.
She texted, 'I have to tell you something!' Then she disappeared. I yelled at the sky.