Quote Originally Posted by lemoni View Post
Спасибо.

Подобным образом, мы говорим
- Почему ты не позвонила вчера?
- Ну я звонила, но никто не отвечал?
In this example "звонила" implies a repeated action (maybe she called them 2, 3 or more times, but no one still picked up the receiver). That's why imperfective aspect is used here. She could have said "я позвонила, но никто не ответил", and that would have meant that she had called them just once, and having gotten no response, she decided to piss on making more calls.