Call someone back by hovering over a voicemail and selecting Call or by selecting More actions and choosing Call back .
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.

Sometimes, when the phone is not picked, the caller is automatically redirected to the voice mail. That means that when someone calls you, he or she will hear some dial tones before going to the voice mail where they could record their message. In Verizon, you can actually set the number of rings before voicemail.
Hello, this is (name). I am sorry I can’t come to the phone right now. Leave your name, number, and a short message after the beep. Oh and please do wait by the phone till I call you back. Bye.