That's according to Glenn Tenney, a computer security expert who posted his experiences and findings onto a mailing list maintained by Dr. David Farber, the famed professor of computer science at Carnegie Mellon University.
Tenney wrote that he discovered the problem over the past few weeks when we'd call his own AT&T number and find out that he had several unheard messages--from one to four days previous--that weren't listed in his iPhone's visual voicemail.
"I just spent 1.5 hours on the phone with AT&T level 1, a supervisor, then level 2 support only to find out: Level 2 support tells me that this is a known issue, has been known since before the 3GS came out and potentially applies to all iPhones -- 1st generation iPhones with V2.x OS as well as 3G and 3GS phones and v3.x OS," Tenney wrote.
"Yes, potentially every iPhone in the entire USA might be experiencing (this is what the level 2 person told me) delays (of days) in having voicemail populate to your visual voicemail. Their ONLY suggested 'workaround' is to press and hold the '1' key which calls your own cell phone and goes into the regular voicemail system and listen to hear if you have any unheard messages."
I cannot independently confirm what Tenney states, though I have no reason to doubt his story. I have actually had the experience myself of having older voicemail messages I'd never seen before suddenly appear in my iPhone's visual voicemail.
This was months ago, however, making me think the problem has been going on for a long time, rather than "weeks" as Tenney posits based on his experience.
"It boggles my mind that (a) this has been going on for weeks in the entire country, and (b) that level 1 support knew nothing about it," Tenney concluded.
I only know about my own experiences and Tenney's. If you've had this problem, please leave a comment below and I'll follow-up.