You can record custom voicemail greetings using your iPhone.
To setup a custom voicemail greeting for your own extension:
1. Launch your App on your iPhone.
2. Tap on the Gear icon in the bottom left part of the screen to view the Settings screen.
3. Tap My Inbound to display the My Settings screen.
4. Tap Messages.
5. Tap Greeting.
6. Tap Custom to create a custom voicemail greeting.
7. Tap Record to start the recording process.
8. Speak into your iPhone and state your customized voicemail greeting.
9. Tap Stop to finish recording.
10. Tap Play to listen to your recording. You may re-record a new message and try again, if needed.
11. Tap Save to complete and save your recorded voicemail greeting.