You can record a custom greeting for your voicemail or use the default greeting for Google Voice. Record up to 10 voicemail greetings and select the one that you want callers to hear. Record a new greeting. When you use the Google Voice app, you can record a greeting up to 3 minutes long.
Open the Phone app. Tap the Voicemail tab in the lower right-hand corner of the screen. If Visual Voicemail is not set up on your iPhone, you'll see a button that says, Set Up Now. Tap that button. Enter, then confirm a custom voicemail password. Tap Custom if you want to create your own custom greeting when someone reaches your voicemail box.

However, most networks do allow you to adjust the length of time that the phone rings before switching to voicemail by dialing in a long code number. On Vodafone this is **61*121*11* followed by the number of seconds and then the hash symbol (#). So to set your phone to ring for 20 seconds you’d dial **61*121*11*20*.
Samsung smartphones are quite famous for offering dozens of additional features that are usually not available on phones with stock Android software and iPhones. The company’s new One UI software not only looks brilliant in terms of design but also offers plenty of useful features, including the ability to record calls.