A professional voicemail greeting is a recording that informs clients and business partners you are not available to receive their call. It is an essential part of any effective business communication strategy, especially if you are in sales.
AT&T: If you’re an AT&T customer, you have the option of creating your own basic voicemail. You’ll need to press and hold the 1 key down while you’re on your phone. AT&T will then ask you to set up your greeting via voice prompts.

Select the Voicemail tab. Below "When callers reach my voicemail, play my," select one of the following types of voicemail greetings: System Greeting - Plays a system generated message that utilizes your recorded name and is the default setting for all new users. Personal Greeting - Plays a custom message that you record using a phone.
Android phones can access voicemail by holding down the 1 key on the dial pad until the phone dials your 10-digit phone number. You will automatically connect to your mailbox and be prompted to enter your temporary password; this password is the last 4 digits of your phone number followed by the # key. Start the Google Voice app. Tap the three horizontal lines at the top left of the screen (sometimes called a hamburger menu), and then tap “Settings.” In the Voicemail section, tap “Voicemail greeting.” Tap “Record a greeting.” How do I access my voicemail? To call your voicemail on an Android phone, simply open your phone’s dial pad and hold your finger down on the “1” key. You can also call your voicemail from a different phone by calling your own number and tapping the pound key. How do you check your voicemail?