The file is a proprietary theme package format developed by Nokia for its Series 40 (S40) mobile platform. These files are essentially compressed ZIP archives that bundle all the assets needed to customize a phone's visual and auditory experience, including wallpapers, icons, and ringtones. Technical Overview
(e.g., Nokia 5310): High-contrast colors like red and blue with musical motifs. nokia original themes nth
You’d send the .nth file to a friend via infrared. Two phones, lined up perfectly, glowing red beams in a dark bedroom. Transfer complete. They’d install it. Smile. The file is a proprietary theme package format