You know that app you use for sexting? Its developers would rather you not sext with it. In fact, considering the iffy legal issues surrounding sexting and "intimate photo sharing," most apps used for the act specifically discourage users from partaking. Just read their terms of service.
Take Facebook Poke, for example. Facebook's legal terms state that users should not post content that "is pornographic; or contains nudity." It'd certainly be no surprise to Facebook to hear that some users don't exactly follow this suggestion to the letter.
In fact, if you look in your phone's app store, you'll likely see the growing number of apps offering private messaging and sharing. If you happen to be looking for apps to use for private, discreet messaging (sexual or otherwise), we've compiled a list of some you may be interested in.