Technology has a nasty habit of becoming ever more complex as we become ever more reliant upon it. More complex equals more vulnerable.
A backhoe and service maps for a city and a terrorist could bring it to its knees. Water, communications and power do not like people digging holes in the ground in their immediate vicinity. Even in the countryside, set up a rig or start excavating near a pipeline and little whirly birds tend to fall out of the sky disgorging rather irate officials. We wont even talk about hacking the control systems for a city's infrastructure.
Yup. City dwellers are vulnerable. The loss of cellphones is the least of the vulnerabilities. Having spent a period of my life involved in geotechnical investigations all over the UK I have a little firsthand knowledge of how much chaos can result from excavations in the wrong place (generally as a result of inaccurate service maps) I can recall one site in rural Wales where both the water authority and Telecom officials were present to show where their respective services ran. The first bucket wiped out the phone line, the second the water supply. Sometimes you cannot win. Trashing fibre optic cables along a motorway is another big no-no. The list is a long one and some were biggies.. Big cities are very, very vulnerable.