This is from this Nintendo link, but it doesn’t quite answer your question I guess. it just says wireless communication is not made. NOT internet communication, but wireless.

“PictoChat is not an Internet application, and therefore is not monitored. PictoChat depends on wireless communication so it only allows you to chat with people within approximately 65 feet of your Nintendo DSi. This means PictoChat does not block messages from strangers. Parental Controls: You can block access to the PictoChat application (how to).”

Hmm found that when I first started looking,