From the separable prefix *an-* ("toward, at") + *rufen* ("to call, to shout"), itself from Old High German *ruofan*. The compound literally means "to call at" someone — making contact by directing your voice (or, later, a signal) toward them. The telephonic sense developed naturally in the 20th century alongside the spread of the *Telefon*.

German has a strong preference for the separable-verb structure: in a main clause, the prefix *an-* splits off and moves to the end — *Ich rufe dich an*, never *Ich anrufe dich*. This trips up many English learners. Also note that Germans often answer the phone by stating their surname — *Schmidt* — rather than saying "Hello," which can catch foreign callers off guard.