Purpose: Mobile social media (MSM), an interaction, exchange of information and creation of user-generated content, mediated by mobile devices, is becoming the locomotive that drives forward evolution of the online world. Fewer academic studies have touched upon the MSM subject, with all the papers being of a conceptual nature to provide recommendations to business-to-business (B2B) firms. This paper aims to explore how B2B firms use MSM in reality. Design/methodology/approach: This paper adopts the grounded theory approach to analyse interviews conducted in 26 B2B firms representing the UK advertising and marketing sector. Interviewees represent key decision-makers who understand the aspects of mobile technology use in their firms. Eighteen firms stressed the importance of social media as a trigger to adopt mobile devices. Follow-up data collection in these 18 firms focus on strategic orientation, processes, routines and skills required for using MSM. Findings: This paper found that marketing and advertising firms use MSM for branding, sensing market, managing relationships and developing content. MSM is treated by businesses as a strategic firm-specific capability that drives firms’ competitiveness, where imitation of such capability by competitors is limited because MSM skills are specific to individuals within organisations and MSM routines are manifested as a result of firm-specific MSM skills’ interactions. Originality/value: This study is amongst the first to provide insights into B2B firms’ practices of using MSM. Additionally, the research is novel because it discovers that MSM capability is developed as a result of the overlap between individuals’ and organisational knowledge and memory, contradicting existing theory on the subject.