If a phone rings once and then goes to voicemail or rings only briefly, it usually means either that your call is blocked or that the phone is not receiving calls at all. If the phone rings five times and then voicemail picks up, it's more likely that the person on the other end simply isn't picking up the call.
If your carrier supports the iPhone voicemail feature, you can retrieve and listen to your voicemail right from within the “Phone” app and call your contacts back by simply tapping their messages. That type of functionality is pretty neat and useful, because it saves you actual time. If not supported by your carrier, you will not be able to see the visual overview of your voicemail inbox and use any of the related features. Tapping the “Voicemail” tab in your “Phone” app will simply call the number associated with your voicemail box. So let’s get going with creating our custom voicemail greeting on iPhone! How to record your own Voicemail on iPhone Phone → Voicemail → Greeting → Custom → Record → Save

While recording a message, make sure that you don’t yell into the phone and make sure you record in a quiet place. Setting this up in a restaurant will make your iPhone voicemail greeting sound like you are actually picking up the phone.
Several users are getting the “com.apple.mobilephone error 1035” error on their visual voicemail whenever they try updating or setting up their visual voicemail greetings. Visual voicemail lets you view your voicemail message that you receive. Voicemail greeting is the message that callers will hear before they are offered the opportunity to leave you a message. However, this error will prevent users from setting up their greetings. The full error message will be “The operation couldn’t be completed (com.apple.mobilephone error 1035)“.