This study explores how police detainees in Australia use mobile phones within the illicit drug market. Fifty-nine percent of respondents had used mobile phones to buy, deliver or supply drugs, mainly through phone calls, text messages or messaging apps. Detainees who had used apps for drug buying or supplying were on average significantly younger than those using other phone-based services for drug buying or supplying. Drug suppliers were significantly more likely than drug buyers to have used messaging apps. Respondents used messaging apps for convenience and to conceal their activities. Almost 50 percent of drug suppliers report having stopped using mobile phones because of law enforcement’s ability to intercept communications.