This paper empirically explores the role that mobile devices have come to play in everyday practice, and how this links to demand for network connectivity and online services. After a preliminary device-logging period, thirteen participants were interviewed about how they use their iPhones or iPads. Our findings build a picture of how, through use of such devices, a variety of daily practices have come to depend upon a working data connection, which sometimes surges, but is at least always a trickle. This aims to inform the sustainable design of applications, services and infrastructures for smartphones and tablets. By focusing our analysis in this way, we highlight a little-explored challenge for sustainable HCI and discuss ideas for (re)designing around the principle of 'light-weight' data 'needs'.