Although the number of older adults with access to landline and mobile phones has grown in recent years, little research exists that investigates how older adults use and potentially combine the two technologies for communication with the members of their social support networks. Therefore, this study explored how the composition of older adults' social companionship networks is related to the frequency of landline and mobile phone communication with their network members. In addition, the study examined the association between landline and mobile phone communication as well as their relationship with in-person communication in such networks. The survey data were gathered using an ego-centered social support approach in a nationwide representative sample of retired older adults in Slovenia. The results of multiple regression analyses revealed that the composition of a social companionship network better predicts the frequency of landline rather than mobile phone communication of older adults with their network members. The non-significant relationship between the frequency of landline and mobile phone communication suggested that the two technologies very likely have a different role in the maintenance of social companionship networks. The study also found a difference between the importance of control variables related to the socio-demographic characteristics of older adults for the frequency of landline and mobile phone communication. While age, education, and living alone significantly predicted the frequency of mobile communication with older adults' network members, significant predictors of their landline communication included gender and health impairments. •Two forms of communication in socializing networks of older adults are examined.•Mobile phone communication is more frequent than landline phone communication.•Network composition better predicts landline than mobile phone communication.•Mobile phone and landline communication supplement each other.•Sociodemographics of older adults are associated with both forms of communication.