The main motivation of this diploma thesis is a development of Android application, which helps user of application to find out who is the owner of unknown phone number. Data source for finding unknown phone number are free available web sources. Through the development of prototype, data from different web sources were integrated. Result of this integration is shown in Android application. Data integration includes access to semi-structured data on web portal of Phone Directory of Slovenia, Business directory and connection with social networks Facebook and Twitter. These web sources represent decentralized database, which is used by web service for searching unknown phone number and querying different data about unknown caller on social n...