You might also consider giving them the option to skip your voicemail message completely by pressing another key (again, check with IT). You also want to make callers aware what you will return their call, instead of telling them that you will try to return their call--and let them know when you are likely to do it, if possible. If necessary, provide additional or emergency information in your voicemail greetings. My dentist, for example, lists his cell phone number for emergencies.
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.

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.
Apple Visual Voicemail is available for free for all Truphone iPhone customers with a data plan. Truphone does not charge an activation or monthly service fee.