Parents Are Listening Services and WebSafety Inc are effective parental control tools for cellphones.

Children using cellphones is becoming so common and treated as a normal thing that the dangers associated with the technology are overlooked most of the times. A lot of parents don't even give it a second though until they heard something really bad has happened to someone somewhere. The true of the matter is that if you are a parent with children using cellphones, the list of questionable behaviors is a long one and still growing. From communicating with unauthorized adults, to exchanging inappropriate text messages, to bullying their peers to using their phones to cheat on class room tests, the pitfalls from kids with cellphones, abound.
The good news is cellphone companies have long offered some levels of control to parents. For instance, Verizon Wireless offers an age-rated content filter for mobile-Internet content.
T-Mobile USA can block certain kinds of messages, such as text or instant messages, while AT&T Inc. can ban specific numbers. All of the carriers offer some form of family locator's feature for roughly $10 a month, the Wall Street Journal says. But there is a catch: for legal reasons, phone carriers can't monitor text messages and emails contents going to or from a cellphone.
Fortunately, some start-ups and small technology companies are stepping up and offering some alternatives.
The Wall Street Journal has reviewed the services offered by a couple of companies: Parents Are Listening and WebSafetyInc.
"Parents Are Listening Services is testing a service that alerts parents when messages containing keywords such as "suicide" or "drugs" are sent to their child's phone. The program, called Kid Phone Advocate, captures the text messages as an image and automatically scans for those words. The company plans to officially launch the program in September for $9.99 a month. The application can be downloaded on most smartphones and basic phones that have an Internet connection." the Wall Street Journal said.
For its part, WebSafety Inc., offers a similar monitoring program that's been available for five months. The company's software draws from a unique library of 6,000 phrases deemed inappropriate, including slang and online abbreviations.
The program can monitor text messages, emails, instant messages and updates to social-networking sites such as Facebook. By using the phone's Global Positioning System, or GPS, features, parents can also set up no-text zones, such as on school grounds, to prevent students from using their phones to cheat on tests or taunt classmates. WebSafety Inc's service called CellSafety is offered either for a single phone for $9.99 a month or for an unlimited number of phones for $39.99 a month.
WebSafety Inc's CellSafety app works on a number of smartphones and basic handsets, although it's not available on Apple Inc.'s iPhone, since third-party developers can't yet access the device's GPS functions.

For more, see WSJ.com