A few notes that require answering?

• You might get a special one for Dad
• Annoying thing to hear in a movie theater
• Caller ID, perhaps
• Bars for a cell?
• Cellphone alert
• Musical cycle has style and contemporary sound
• Nitrogen affected sound of handset
• Sound heard when someone telephones
• One's heard on the phone offering to negotiate, to some extent

Wiktionary Word definitions in Wiktionary
alt. the sound made by a telephone when ringing, especially the customizable tone of a mobile phone n. the sound made by a telephone when ringing, especially the customizable tone of a mobile phone