If you want to avoid marketing calls, you can just block them instead. This won’t stop that first call, but it will stop subsequent calls.
With all the amazing different types our iPhone’s can do, we sometimes forget they are also a phone. While calling people isn’t nearly as common as it once was, it still happens and your phone still needs to be able to make and receive calls. However, there are bound to be times when you are not by your device when a call comes through. But instead of just missing the call entirely (which could be incredibly important), why not set up voicemail on your device. While it might sound like a daunting task, it really isn’t that bad or hard to create. However, if you are confused about how to set up voicemail on your iPhone 6S, worry no more. This article will go into how to set up your voicemail on your device with ease.

If you never recorded one and want to record or change a voicemail greeting, you've come to the right place. The process is very simple. You'll just have to click the green phone icon, the same place you make calls, and navigate to the voicemail screen. On the voicemail screen, you'll see a greetings option on the top left.
Open the Phone app. Tap the Voicemail tab in the lower right-hand corner of the screen. If Visual Voicemail is not set up on your iPhone, you'll see a button that says, Set Up Now. Tap that button. Enter, then confirm a custom voicemail password. Tap Custom if you want to create your own custom greeting when someone reaches your voicemail box.