zhèyàng duìfāng bùyòng cóng tóu jiǎng, yě zhīdào nǐ bùshì gùyì guàduàn

这样对方不用从头讲，也知道你不是故意挂断。

This way the other person doesn't have to explain from the beginning, and they know you didn't hang up on purpose.