Voicemail won't play until moved into the "deleted" folder.

I am also having this problem. I highlight the message and hit the arrow on the far left to play the message, and nothing happens. I can listen to the message once I "delete" it. I have to go into "Deleted Messages" and then I can play it from there. I can also "undelete" the message, and it plays just fine from the Voicemail list. It just seems to be brand new messages that are the issue. Any ideas on how to resolve this?

I have this exact same issue on my sprint 4s iPhone. It is very frustrating.

To further expand on this the messages show as having -0.00 length to them. If you delete them then go into the deleted folder and press the play button they will thin have the spinning indicator that they are downloading and it will show the actual length and play them fine. You can then undelete them and they will play in the regular folder. But I have found that eventually they will go back the way they were and show zero length again and you must repeat the process to play them again.

It is as if they are not downloading to the device.