Most of the time, an update to your carrier’s voicemail app or settings will cure the issue; however, it is important to confirm that your voicemail number is appropriately configured before proceeding any further.
Navigate to your Phone app located at the bottom of your iPhone home screen. Tap-open the Phone app. Once you have done that, you will see a voicemail logo the bottom right corner of the window that has opened, select that voicemail icon. That action will open the visual voicemail interface. At first, all you will see is a blank screen with a

Great question! Although I don’t know if there is a specific function for this on your particular phone, the best way to save the message is the simplest. Turn up the sound as high as you can and record it onto a digital recorder (like you would use for a lecture), a cassette recorder or your cell phone if you have a voice recorder on it. Then save it as an MP3 on to your computer for safe keeping. You can also Google your vtech model number to see if you can find an owner’s manual. They might have a way to save a recording in there. Probably not, but it’s worth a shot.
I know you’re thinking what does recording an iPhone call have to do with voicemail, but it turns out that a simple trick allows you to use the service to record any phone call, and it works great. Not only will you get the recorded phone call, but you’ll be able to save and share the call recording as an audio file as well.