This is an intricate phone scam. Unknown number calls you and then leaves a voicemail (which is rarer for scams) notifying you of a contest you *may* have entered within the last 8 months. Note the message below that is left on the voicemail. It never indicates a name or direct phone number nor does it give you a number to call back that shows up as a registered sweepstakes call center. Avoid - it's a phishing attempt.

"Hi Jayland here with the gift redemption department giving you a follow up call in regards with the $25,000 cash summer giveaway that was sponsored within the last 8 months. We're looking at your name and number we have very good news for you what we need you to do as soon as possible is to give us a call in here toll free in the office 1-888-510-5221, again that's toll free 1-888-510-5221. We do need to hear from you as soon as possible and congratulations!"