If you don’t make any changes the default iPhone voicemail message is pretty bland and not very professional. It is a good idea to change the iPhone voicemail message to something more professional or at least something that lets callers know they reached the right person.
Alternatively, if you simply want to alter your voicemail message to something else, you can do so.

That way you'll get to know exactly what other people hear when they call your phone and one last thing I wanted to show you. If you don't see that play on record option on the bottom, you don't have visual voicemail. Set up on your phone and that's through your provider. So if you have at and T sprint T-Mobile or any other provider, you need to have visual voicemail.
2. Press and hold the "1" key on the keypad. If it’s your first time setting up voicemail, you’ll likely see a message that says “No voicemail number is stored on the card.” If pressing this button dials your voicemail service, listen to the prompts for instructions on completing the setup process.