You can tap on Record to start recording a new iPhone voicemail greeting and then Stop when you are done. Tap on Play to listen to it so you don’t have an embarrassing mistake or noise in it. When you are satisfied with the message, tap Save in the upper right.
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?

Once you click greeting, you can change it from default to custom and record your custom greeting. Press play to listen to it before saving it.
Important: In some countries or regions, deleted messages may be permanently erased by your carrier. Your voice messages may also be deleted if you change your SIM card.