Mobile health (mHealth) interventions have the potential to improve substance use treatment engagement and outcomes, and to reduce risk behaviors among people who inject drugs (PWID). However, there are few studies assessing mobile technology use among PWID and none have investigated continuity of mobile phone use. : We surveyed 494 PWID. We used bivariate (independent-sample t- and chi-square tests) and multivariate (logistic regression) analyses to determine whether mobile phone and/or internet use differed as a function of participant- and/or injection-related characteristics. : Most participants (77%) had a mobile phone, with 67% having a phone that was free of charge. Participants with a phone were significantly less likely to be homeless (AOR = 0.28), to have shared syringes (AOR = 0.53), and to have reused syringes (AOR = 0.26) in the past 3 months. We observed high rates of phone and number turnover, with more than half reporting that they got a new phone (57%) and/or number (56%) at least once within the past 3 months. Most participants were familiar with using the internet (80% ever use), though participants who had ever used the internet were younger (AOR = 0.89), were less likely to be homeless (AOR = 0.38), were less likely to have shared syringes (AOR = 0.49), and were more likely to have injected methamphetamine by itself (AOR = 2.49) in the past 3 months. : Overall, mobile technology and internet use was high among our sample of PWID. Several factors should be considered in recruiting diverse samples of PWID to minimize bias in mHealth study outcomes, including mobile phone access and protocol type (text- vs internet-based).