Configuring the answering system, including the number of rings (often adjustable between 2 and 6 rings, or "Toll Saver" mode), as explained in this VTech support video .
This is useful for conference calls or voicemail systems. While on a call: vtech cs2051 manual
: Using the 30-entry phonebook, caller ID (stores 20 calls), and hands-free speakerphone. Configuring the answering system, including the number of