It could be redone. The first solution is Case walking by a line or some other linear crowd and, as he walks, the closest cellphone rings, then the next and so on. I wouldn't do cell phones, but Fringe Redverse-like earpieces. Rings, in that scenario, would also feel weird as some other form of warning would be employed. A series of hello's and reactions to dropped lines, as Case turns back and realizes someone really wants to talk to him. Then he would walk up to a kiosk, and buy a discardable phone that would, immediately, ring.

I would try to avoid the phone-in-an-envelope scene in Matrix, but someone perplexed could hand him a phone and say "it's for you".