Social media services, including Facebook, have recently grown to be a substantial part of everyday communication for hundreds of millions of people. Mobile technology has evolved to a point where a modern smartphone can be constantly connected to the Internet, facilitating straightforward communication via mobile social media services. This can introduce service substitution, where users communicate through these services instead of mobile operator provided calling or SMS services. In this article, we have studied Finnish Facebook users and their mobile Facebook usage with quantitative methods. Based on a review of the existing research, seven hypotheses are proposed of which six have statistical differences when comparing modern smartphones and older phones. Using this comparison, the results include evidence of Facebook mobile being a substitute to the traditional calling and text message services, as well as the importance of push notifications. Based on the results, further research areas are proposed. Keywords: Social media services; Mobile application usage; Service substitution