An article attributed to the US Federal Communications Commission addresses the issue of adult content being made available to children via mobile devices, and what parents should be aware of and can do about it. “Adult material is available through numerous sources, including magazines, television, movies, songs, telephones, gaming systems, and the Internet. But neither a blocking technology - like those used on televisions, telephones, and home computers - nor a ratings system - like those used for movies, games, and music - has been developed for wireless phones/devices. The wireless industry is working to address these issues, and the FCC is monitoring the situation.”
The advice seems pretty good, such as monitoring how children use the phone (whether primarily for voice or for data) and checking the phone bill for unusual downloads. It also suggests calling the phone company to find out what content is available on the childs handset and plan and whether it can be restricted.