Changing default voicemail to the custom greeting is very simple until iPhone won’t save custom voicemail greeting or custom voicemail greeting on iPhone not working issue arises. Don’t worry, you are not the only one with this problem, till now many users have fixed the unable to change voicemail greeting on iPhone with the help of below solutions.
The telephone systems have the feature named as Voicemail. VoIP is the best example of it. When a receiver is unable to pick up the phone, then the caller can leave the voice message on the receiver’s phone. In older telephonic machines, such messages were stored as a voice message directly, and the receiver can hear them later. In modern telephone systems, such info is being stored on the server of the service provider in the user’s mailbox. It is similar to email in which the messages are saved in the form of audio instead of text.

When you reset network settings, all of your iPhone’s Wi-Fi and cellular network settings will be erased. This includes your Virtual Private Network (VPN) settings, your Bluetooth devices, and your Wi-Fi networks — so make sure you write down your passwords first! We do this step because it can be very difficult to track down the exact source of a software problem, so we reset all network settings.
It comes with a SIM card. Yes Iphone 12 comes with the Sim Card included you don’t have to buy anything my phone came with the Sim Card and at best buy they helped me install it they set it up and transferred everything from my old phone to the new phone when I left the store phone was ready to use.