Series of notes calling for an answer? (8)
I believe the answer is:
ringtone
'series of notes calling for an answer?' is the definition.
(musical notes heard before you answer the phone)
This is the entire clue.
(Other definitions for ringtone that I've seen before include "Sound coming from mobile" , "Sound of modern life" , "Sound heard when someone telephones" , "Sound made by a mobile phone" , "announcement of caller" .)