Living in an informal settlement with a visual impairment can be very challenging resulting in social exclusion. Mobile phones have been shown to be hugely beneficial to people with sight loss in formal and high-income settings. However, little is known about whether these results hold true for people with visual impairment (VIPs) in informal settlements. We present the findings of a case study of mobile technology use by VIPs in Kibera, an informal settlement in Nairobi. We used contextual interviews, ethnographic observations and a co-design workshop to explore how VIPs use mobile phones in their daily lives, and how this use influences the social infrastructure of VIPs. Our findings suggest that mobile technology supports and shapes the creation of social infrastructure. However, this is only made possible through the existing support networks of the VIPs, which are mediated through four types of interaction: direct, supported, dependent and restricted.