The basic rule of thumb is that callers should hear one of two things when they first connect with your voicemail — either an apology for not being able to answer the call or a “thank you” for having called. You can do both if you prefer, but keep it short and to the point.
Enterprise level organizations can use professional voice mail prompts to establish brand and consistency. Smaller organizations and even one person firms can represent themselves as a professional and established organization that understands how to present themselves to the business world and their potential client base.

To set up voice mail, tap the Phone icon, tap the Voicemail icon and then "Greeting.". There are two options available: Default and Custom. If voice mail hasn't been set up previously on your phone, Default is selected, which means people will hear your wireless carrier's generic voice mail greeting when they call you.
My Visual Voicemail is a free app that can be used since its first launch without changing your voicemail number. Simply add the widget to your home screen by long-pressing the space on free space and choose My Visual Voicemail. Now you can get easier access to voicemails. Navigate to unread messages and you will never miss important messages anymore.