The components of your request suggest a few possible areas of interest, though none combine into a single recognized "essay":
In a technical context, this often refers to directory services. In software or data science, a "telefonbuch" might be a dataset used for testing or a specific mobile application file (as indicated by the .ipa extension). download-mmm3-telefonbuch-ipa
This is the file format used for iOS (iPhone/iPad) applications. The components of your request suggest a few