I think Whispering Winds should be able to target areas within the Mist. Chances are the person/people you wish to contact with the spell will more likely be within the safe confines of the Mist anyway.
Umh, didn't know it doesn't yet. Guess there are probably really good ic reasons to limit it that way though, otherwise it's hardly worth the work of implementing a limitation like this.
Your reasoning makes sense however.
I'm inclined to think the limitation is due to the spell sharing the same crafting menu as the teleportation spell.
Even though I'm glad teleporting has been banned from the mist areas due to the OOC consideration that it was being rather overused in EFUA, the same certainly doesn't go for whispering winds, a spell that could probably do well with being usable within the shroud.