The Android operating system includes a native visual voicemail that lets you view voicemail messages in text form. If you have an older Android phone or if your service provider doesn’t offer visual voicemail, you can download a third-party app. Select Phone. Select Keypad. Press and hold the number 1. If your voicemail is not set up, select ADD NUMBER. Select Voicemail number. Enter the Voicemail number and select OK. Repeat steps 2-4 to check your voicemail.
Your AT&T VoiceMail Service access number is: 1-888-288-8893. When calling from home, if prompted, enter your password followed by #. If you are not calling from home, you will be prompted to enter your 10-digit telephone number followed by your password, then just follow the system prompts. From any Home screen, tap Phone. Touch and hold 1 or dial 123 and tap Call, or tap the Voicemail icon to call voicemail.

On the iPhone, go into voicemail and tap "Greeting". Record a few seconds of something and tap stop. Before you tap save, use iFuntastic or SFTP to navigate to /var/root/Library/Voicemail on your iPhone. You'll see a file called "Greeting. amr". This is the audio you just recorded. Delete that file and replace it with your custom message which should then be renamed to "Greeting.amr". Tap "Play" on the iPhone to verify your message works. If it plays, tap "Save" and your custom message will be uploaded to AT&T's servers.
Perhaps one of the biggest changes with the iOS 9.2 update is that it fixes a lot of iOS 9 problems and iOS 9.1 problems for iPhone and iPad users.