Step 5. In the greeting section, select whether you want the greeting to be default or custom. Choose custom if you want to record your own voice for a personalized greeting.
Alright let me try to clear this problem as much as I can. From the parent carrier, we have a limitation or you can say a requirement that all numbers should have the Voicemail set up. So what we do for those customers who don’t want it, we disable it from our side but again the numbers keep syncing from the parent carrier’s network from time to time (roughly once a quarter). When the numbers get synced, voicemail automatically gets enabled. To some people, this is alright but sometimes it becomes inconvenience for the customers to call us again to disable it.

If you’ve already created a custom voicemail on your iPhone, you can tap Play to see how your voicemail sounds. If you’re interested in creating a new message, tap the Custom button. From here, you can start recording your message by tapping Record and tapping Stop whenever you’re finished. Once you’re finished recording, tap on Play to make sure the message comes across as you’d like and hit Save (in the upper right) to save it as your voicemail.
Verizon only: Unfortunately, if you have set up the voicemail successfully but still unable to change the greetings of Voicemail from the Voicemail tab, then dial *86 and select option 4 to make a change. Step #1: Launch the “Phone” app on your iPhone. Step #2: Tap “Voicemail”. Step #3: Select “Greeting” on the upper-left corner of the screen. Step #4: In case, you are also using eSIM then select the second network to change voicemail greetings. Step #5: Select “Custom”. From here you can record a greeting. Step #6: Tap “Record”.