them, in bold type refers to:

PRISONS AND MOBILE PHONES

Bricking the intruders

If mobile phones can’t be kept out of prisons, can they be made useless?

Oct 14th 2010 | RAIFORD, FLORIDA AND PARCHMAN, MISSISSIPPI

THE striking thing about mobile phones in American prisons is not that they exist—though they do, in great numbers—but the ingenuity used to get and keep them. There are the usual entry methods: from visitors, corrupt guards or in packages hurled over the fence. But phones often take more exotic paths. In South Carolina a potato gun was used to fire phones over prison walls from a distance of a third of a mile. In Mississippi a suspiciously heavy and bounceless basketball in the recreation yard was found to contain 19 phones and chargers. (…)

Available on http://www.economist.com/node/17257847?story_id=17257847, accessed on November 4, 2010