Can I retrieve a deleted voicemail

So I'm guessing that you deleted the voicemail, and then cleared it from the Deleted List. If that is the case, I'm not sure, but if you were to restore your phone to a backup that was made while the voicemail was on there, you may be able to recover it. I've never tried this before, but it would seem to be feasible. Otherwise, visual voicemail is from your carrier's server, and once downloaded to the iPhone, it is removed from the server, so there is no other location to try and recover it from.