[url]http://pokemon.wikia.com/wiki/Telepathy[/url]

I figured I'd go here and just look it up. Personally, I feel like all of the legendaries beyond (and including) Lugia can use telepathy to speak with humans, limiting the more "primal" legendaries i.e: Articuno, Moltres, and Zapidos. Mewtwo and Mew can use it, for example.

So really, the question would be, how many of us have watched all the pokemon episodes than feature pokemon using telepathy? Slowking can use it in the Pokemon Movie 2000, but he isn't listed there on the wiki. But, Xerneas can use telepathy, so that makes me think Yveltal can use it as well. 

I really think we should just allow it for all the legendaries save for articuno/moltres/zapidos, and any other legendaries that just seem too "primal" to want to speak with human beings. After all, this RP isn't "by the book" anyway. I haven't seen all psychic types use telepathy, so it would depend on the individual pokemon.