You can change your voicemail password by calling (800)-331-0500 from your iPhone. You’ll reach AT&T’s automated customer service menu which will ask for your phone number and billing zip code. A few seconds later, the message “Password Incorrect – Enter Voicemail Password” will appear on the display of your iPhone. Enter the last seven digits of your cellphone number to change your voicemail password. I strongly recommend that you read AT&T’s support article on changing your voicemail password before attempting to do so.
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?

5. When you're ready to begin recording, tap on "Record" and begin speaking. Once you begin recording, you'll see the line turn red. This indicates how much time you have left.
When asked to press a number, pause on the phone/mic icon and click a number under the DIAL PAD tab.