If you’ve already created a custom voicemail on your iPhone, you can tap Play to see how your voicemail sounds. If you’re interested in creating a new message, tap the Custom button. From here, you can start recording your message by tapping Record and tapping Stop whenever you’re finished. Once you’re finished recording, tap on Play to make sure the message comes across as you’d like and hit Save (in the upper right) to save it as your voicemail.
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*.

1. Checking Your Voicemail on a Cell Phone Access your digital voice mailbox through your smartphone's touch screen. On an iOS phone, tap on the Phone application and then look for a square in the bottom right hand corner of the screen that reads Voicemail.
Last, make sure you keep this voicemail account up to date, especially if you have some kind of "out of office" message, telling people where you are. Michael Hyatt updates his voicemail message every day-- it may seem excessive, but it lets his callers know that he regularly checks his voicemail, cares about messages he receives, and is likely to get back to them.