Civil engineer here, we often use recycled aggregate (gravel sized bits) in concrete nowadays. You'd be surprised how much random stuff makes its way into the mix, because it often comes from demolished buildings. Anyway, the other day we were wondering what might happen if an old Nokia 3410 made its way in there. The consensus was you'd probably be able to ring the number for a good week of two and spook people... I really must try that sometime!