People in Cambridge can now alert the CCTV centre via SMS. As the article notes, "there are something in the region of 170,000 pairs of eyes living, working and playing in these areas - who can see a lot more than the police or CCTV cameras ever can." More details are at the Cambridge site.
The "bigger" issue of why those 170,000 people should just hand over all responsibility for their town to the Police aside, there's one really obvious flaw in this idea.
How do you know that the person sending the text is telling the truth?
CCTV is not all-seeing. Cameras must either rotate, or you must have a number of them in one area (or, indeed, in all areas) to cover a wide space. Assuming the camera isn't hidden, one can be pretty aware whether or not they're being watched by simply looking at the camera.
So publically-directed CCTV means that the public (who are also suspects/criminals, remember) can quite easily influence the direction a particular CCTV camera is pointing in by sending a text. The chances of this working are, according to the site, directly proportional to the seriousness of the offence being reported:
"Please note that an incident involving for example an assault will take a higher priority than a shoplifter."
Thus, in an area covered by only 1 camera, misdirect the camera elsewhere while you carry out whatever crime you want. The level-of-seriousness approach dictates that even if someone does see you and alerts the CCTV room, there's a good chance your faked "incident" will take higher priority over the crime that you're committing.
Does no-one think these things through?