Go to the Settings app, switch Airplane Mode to off, then switch it back on 30 seconds later. If that doesn’t work, go to Settings > General > Reset and select Reset Network Settings. You also might want to try powering down your iPhone and turning it back on. Select the Voicemail tab, then select Set Up Now. Note: Alternatively, you can set up voicemail by selecting the Phone app then pressing and holding the 1 key. If prompted, enter your voicemail password then follow the prompts to set up your voicemail. Go to Settings app → Tap on Cellular Data → make Turn Cellular data ON. If it’s already enabled, then make the turn-off and back on again and however, you have an issue regarding voicemail then try next way.
Now, as for recording your actual voicemail, you will be prompted to say and record your full name as this is the default voicemail of the Samsung Galaxy S9. If you would like to customize it instead to be a personalized message, follow these instructions.

When it comes to making phone calls, nothing can leave one more in the dark than leaving a message on a voice mailbox that hasn’t been set up yet. However, if you happen to be in the dark in regards to setting up your voicemail, we’re going to walk you through the process to avoid confusion on your end. With this being said, here’s a look at how to set up your iPhone voicemail.
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.