Why do we see fines for littering but but not for cellphones ringing in the middle of movies and concerts? I'm afraid the question is better than any answer I have to offer. A private tort suit against the rude and negligent cellphone owner is plausible, but damages are difficult to determine, and the nuisance, though I use the word sloppily, affects many people. The apparent absence of a negligence suit might be attributed to this problem of injury and damage assessment. But the same could be said about a fellow who "negligently" lets a paper bag and its contents fly out the window of his car. In that setting, we resort to fines rather than torts, though that must be in part because the littering is on public property. The cellphone wrong is often on private property, and littering is normally a misdemeanor on public property.
There is also the comparison to smoking, where smoking is banned. Again, a tort suit seems unlikely, but fines for smoking are common both in public places and in private places subject to public regulation. Someone who smokes in a banned area, including a restaurant, in Chicago is subject to a $100 fine; the non-complying owner also faces a $100 fine for the first offense, and then $500 for a second offense. It is not clear what constitutes an offense by the owner, but presumably it is for encouraging rather than working to exclude active smokers. Cellphones could be subject to the same sort of regime; the externalities are similar in terms of the puzzle of why owners do not have sufficient incentive to abide by the majority's preferences, at least in some establishments. The distinction, we might reason, is that a smoker is immediately identifiable, but a cellphone that rings is not. Indeed, it is plausible that fines (or stipulated damages) would worsen the cellphone problem, because violators might not immediately pull out their phones and turn them off, but rather ignore the ringing and allow it to go on, in the hope that no police or owner would be able to pinpoint the source of the disturbance.
A quick internet search reveals many proposals to fine cellphone use or ringing, but few if any enforced fines. There are contexts, such as schools, airplanes, and custom halls, where the rule is said to be that a violation leads to the forfeit of the phone. This suggests a social norm as well as a plan for theater owners and other contractual parties. We might imagine a announcement that if a phone rings during a performance, the owner "ought" immediately pull it out, turn it off, and hand it to an usher or stranger/neighbor who will give it to the box office where the owner might claim it one week later or, more quickly, with the payment of a substantial fine. Again, the idea would be to bring about much greater compliance with the standard of turning off the phone at the outset of the event. And again, there is the danger that phones will ring (less often but) longer to escape detection.
The problem is of course a trivial one as problems go. But it points, first, to the interesting set of behaviors that constitute negligence with no enforcement through tort law and, second, to the problems that generate political pressure for fines (publicly or privately stipulated), even though fines are less calibrated (to the level of injury) than are negligence suits. Charges for overdue library books and film rentals come to mind, and these examples remind us that a "problem" with fines is that some users take them to be prices, and then increase the level of violations. There is the well-known example of a charge for late pickup at a daycare center leading to yet later pickups. But there is also the obvious response in these contexts, that the price can be increased until the "seller" is satisfied with the level of compliance and revenue from the fine. If three cellphones ring during a play, and this finances $10 gift certificates to all patrons as we exit the theater, I doubt we would have many complaints about those annoying cellphones.