Why are mobile phones annoying?

Sixty four members of the public were exposed to the same staged conversation either while waiting in a bus station or travelling on a train. Half of the conversations were by mobile phone, so that only one end of the conversation was heard, and half were co present face-to-face, conversations. The volume of the conversations was controlled at one of two levels: the actors' usual speech level and exaggeratedly loud. Following exposure to the conversation participants were approached and asked to give verbal ratings on six scales. Analysis of variance showed that mobile phone conversations were significantly more noticeable and annoying than face-to-face conversations at the same volume when the content of the conversation is controlled. Indeed this effect of medium was as large as the effect of loudness. Various explanations of this effect are explored, with their practical implications.