Rehearse or write down your message before recording it. Remember that old saying “practice makes perfect?” It’s certainly true when it comes to creating an electronic greeting. The more you’ve rehearsed, the easier the message will be to restate. If you don’t have time to practice, writing down the greeting before recording it – and then reading it aloud from the paper – may help you stay focused on the correct wording.
When I go to set up voice mail, it asks me to enter a voicemail code, add a 4 digit number and then it asks to confirm that code, I hit done and it tells me that voicemail is currently unavailable, try later.

2. Enter the destination you wish to transfer the call to, then press [SEND] softkey. 3. Once the receiving party answers, announce the call. 4. To complete the transfer, press again. If you hang up before the call rings, the transfer will fail and the call will be disconnected. Direct to Voicemail: Transfer a call directly to voicemail 1. Press . 2. If a phone rings once and then goes to voicemail or rings only briefly, it You can't definitively know the cause of a phone barely ringing and going to voicemail because neither a phone company nor the phone's operating system provider will tell you if your phone number is blocked.
Voicemail issues are apparently common across the range of iPhones. I have seen them from the older iPhone 5 all the way up to the iPhone XR. Sometimes it’s not the phone itself at fault, but the network that’s causing the problem. Sometimes it is the phone, and a few simple tricks can get voicemail working again.