Alpern, a designer from San Diego, told ABC that the surprise delivery arrived Monday morning while she was at work.
"My husband sent me a picture of my dog and the box from AT&T, saying, 'I think your phone's here!' and I was like, 'No way! It doesn't come out until Friday," Alpern, 31, said. "I hadn't gotten a shipping confirmation or anything. It just showed up."
The new iPhone 6s will not be released to the public until Friday.
As soon as Alpern got home, she said she backed up her old phone, opened up the box containing the new iPhone 6s and started taking photos and uploading them to Twitter.
"It started getting a lot of traction, and a lot of people were asking me for the diagnostics of it," Alpern said, "so I started testing it out and sharing my findings."
"I love it!" Alpern said. "I think it's fabulous and absolutely fantastic. Shooting in 4K is really unique. It looks like real-life as you're shooting, and the photo quality is amazing. I'm having lots of fun with it."
The designer added that she loves the rose gold color, saying she "expected it to either be a little more pink or a little more gold, but it's actually the perfect combination of both."
Alpern said she isn't sure how she accidentally got the phone early, but AT&T did tweet at her saying, "That's awesome!" and complimenting her five-year-old Yorkie, Ringo, who's featured in one of her 4K video quality tests.
ABC News has reached out to Apple and is awaiting comment.