No, you do not need to use wifi to use the WeddingMix app. We recommend using Wifi or cell service to download the app from the Apple app store or Google Play. But, cell service or wifi is not needed to shoot photos and video on the app. We've had brides use the app in the deep woods of Canada and on islands with no wifi. The WeddingMix app just keeps your files inside, until you or your guests decide to upload.
We do recommend using Wifi to upload because we edit using the full HD files, so they are huge! Your guests can do this at any time within 3 weeks after the wedding. 4G can be used to upload in the settings screen of the app.