Receive up to $504 promo credit ($180 w/Welcome Unlimited, $360 w/ 5G Start, or $504 w/5G Do More, 5G Play More, 5G Get More or One Unlimited for iPhone plan (Welcome Unlimited and One Unlimited for iPhone plans can't be mixed w/other Unlimited plans; all lines on the account req'd on respective plans)) when you add a new smartphone line with your own 4G/5G smartphone on an eligible postpaid plan between 2/10/23 and 3/31/23. Promo credit applied over 36 months; promo credits end if eligibility requirements are no longer met.
My voicemail did the same thing. The problem is caused by contacts that have incomplete information. Three of my contacts had a phone number but the name was listed as unknown. One contact had only a partial phone number.
I went through my entire contact list (yes, it was long) and made corrections and deletions. Then I opened my voicemail app again, and Presto......all voicemails came up.