Skylight only needs WiFi to get set up the first time and download photos to the frame. All other features will work without WiFi.
You can set up the frame for your loved one by connecting it to a WiFi hotspot (using your phone or another tablet that has hotspot access). When the frame is not connected to WiFi, any photos you send will be stored in your server. When you visit, just connect your frame to the hotspot again, and all the photos you've sent will get downloaded!