When you answer calls made to your Google Voice number, tap 4 on the number pad. Participants will hear a robot voice state that recording has begun—this is Google's way of keeping you legal; Alphabet Inc. wants no part of a lawsuit. To stop recording, tap 4 again or hang up. You can hit the 4 key as often as you like to start and stop recording.
On the home screen, expand the App Drawer and tap on the entry named Visual Voice Mail. You’ll be taken through some introductions screens that will showcase some of the capabilities of Visual Voicemail. Tap on Start to configure the service.If you’re a new customer or you haven’t gotten around initializing your voicemail, you will be prompted to do so. But if you followed the first guide, that won’t happen. In any case, after you enter your voicemail password, tap on End Call. After a short waiting period, your Visual Voicemail should now be configured. From the next screen, you can Set your personal greeting or hit Ok to skip this step. To check a voicemail with this service, open the App drawer from your home screen and tap on Visual Voicemail.You’ll see a list with all your voicemails. You can select them All or tap the New tab to only display the ones that you haven’t listen to so far. After you open a voicemail, you can listen to it by tapping the Play icon. To delete a message, tap the trash icon then tap Delete.

Sometimes when your iPhone experiences issues related to your cellular network (no or poor service, calls going straight to voicemail), the problem is stemming from the cellular network, not the iPhone itself.
I got a new cell phone recently. As the world stood in line to pick up the latest iPhone 8, I graduated to the 6S. I pride myself on that actually. As with all new phones in the 21st century, the voicemail must be set up anew. I used the default message for the first few days, but finally settled down to record a more personal greeting.