Some mobile networks automatically set up a default PIN for your voicemail system, which may be something as simple as ‘1234’. That’s really easy to guess, so if someone knows your mobile phone number then they may be able to get into your voicemail just by guessing your PIN.
If you want to record phone calls on your smartphone, you can still do it. You just need to know a couple of tricks—or download a third-party app.

15. Hello, you’ve called [X Business Name]. We are currently closed. Our opening hours are [State opening hours]. Please visit our company website at [company website URL], or email us at [X email address]. If you’d like a callback, please leave your name and phone number, and our team will get in touch with you within 24 hours.
Recording voicemail greetings for your business or personal life requires a separate list of priorities, because they are being used for two distinct purposes and will be heard by two very different types of callers. I have a friend with two cell phones - one for work, and one for personal calls - and if you call both lines, you would never know it's the same person. While the message on his personal line might not be ideal, he took the time to record a professional voicemail message for his business phone, which makes it stand out.