28 Personal Content Experience: Managing Digital Life in the Mobile Age as the eight GB of content could take days to download and cost maybe hundreds of dollars in cell phone fees. Estimating speeds and costs is, of course, hard for non-technical users. The problem gets worse when some of the data resides in networks and some is available locally in the users’ devices. It may not be appar- ent at all to users if they are accessing data locally or over a network. This should not matter at the end of the day, but once the issues of speed and cost step onto the stage, the users suddenly engage them- selves into optimizing data access patterns. Some people go to great lengths with this; others just do not care or simply give up. This is a fundamental problem of mobility: as the technical circumstances vary greatly, it is diffi cult to hide the resulting technical limitations, as users still need to make choices on the basis of these limitations. DAVE, THE BIT PINCHER Dave hated cell phone plans. For one thing, he could not fi gure out why his data bill tended to skyrocket. He had gone with his grandson Eddie to the local Phoney store and settled for the Mr. Data concept, which supposedly was what he needed to access those betting sites via GPRS, while not spending all his wins on the data costs. Eddie had explained that with this deal he could access a total of 100 megabytes per month, included in the plan. Given his usage, the limit would be more than suffi cient. Dave did not have a clear idea of what a GPRS or a megabyte was, but he was happy with the simplicity. Now, something was broken. The connections seemed much slower than usual and the latest bill was more than £100 higher than expected. Dave had ordered the detailed listing from Phoney and then invited Eddie to come and explain it to him. Eddie had showed up promptly, good boy, with his new girlfriend. She watched the tube and conversed politely with Esther while Eddie played Sherlock on the bill, then the phone, then the bill again, and so on. After a while it turned out that, as Phoney had sent Dave a new SIM card, the default data connection settings had been reset. Eddie explained that instead of a native data connection he had unknowingly dialled modem calls, which took time and therefore cost money, while being so slow. Dave felt helpless. How could he have known? Why was new technology so obscure? Give him something that he can hit with a wrench, and he would be happy. If it leaked, Dave could fi x it – but this new tech did not just leak, it was totally broken. Mobility also means that the users’ data moves about in various envi- ronments. Some of these places can be hostile. For instance, WLAN networks are vulnerable to wireless attacks. Mobile devices with WLAN could be exposed to attacks simply by being within reach of a network with rogue devices. An attacker could lurk in a mall waiting for people