Applications on Android phones which block spam calls could be argued a necessity for people unfortunate enough to have their number on spam lists. Third-party applications provide exten- sive, up-to-date blocklists to screen incoming calls. This paper analyses and describes how these types of applications store and access their data. First we analyse which applications keep their data offline on disk, then we take a look at applications which use the internet to query an in- coming phone call. We found four applications use a combination of both, two applications using exclusively online resources and four applications using offline resources only.