silent phone calls can constitute an assault.
Collins v Wilcock 1984
A police woman held a woman's arm to stop her walking off while being questioned. The woman scratched the police woman and was charged with assaulting a police officer in the course of her duty.
Tuberville v Savage 1669
If a threat to harm does not include a present intent to harm, it is not an assault. An assault requires a threat of IMMINENT danger.