5. Switch on and switch off Airplane Mode. You can do this from either Settings or the Control Center. On iPhone X or later, swipe down from the top right of the screen (where the battery indicator is).
Step 7: If you want to record all the calls you make or receive, select the All numbers option. If you wish to record calls from the numbers that are not saved in your contacts, select the Unsaved numbers option. You can even choose some select numbers manually that you wish to record calls to and from by clicking the Selected numbers option, then tapping Auto record numbers, and then add the numbers that you desire by typing them manually or adding those numbers from your Recents or Contacts lists.

It is necessary to record a personal message greeting after you have set up your voicemail number.
At this point, do not insert a new SIM card, or you might lose the voicemails that you saved on your iPhone. (Click to see How to undelete Voicemail from iPhone) 2. Use Automated System to Reset Password (Call 611) Call 611 and enter the wireless number starting with area code. Press 3 to “get help with voicemail.” Press 3 to reset your VM password. Enter the Billing Zip code for your account. In a few seconds, iPhone will prompt you the message "Password Incorrect - Enter Voicemail Password." Enter the last seven digits of the wireless phone number and tap OK.