How can I set a custom per-person ringtones, but for texts and not calls? I know how to set a custom ringtone for a given caller on my phone: pull up the person's entry under People, open the menu and select "Set ringtone." However, this only applies to regular voice phone calls.

Is there a way to do a similar thing for the sound that plays when a "text" &#8212; by which I mean either SMS or MMS &#8212; is received? If so, what is it? The Messaging app's settings only seem to let me choose a single notification sound, but I'm hoping there's something I'm overlooking.
I don't believe that there's a way to do this using the settings in the built in Messaging app, but there are 3rd party apps that can enhance the built-in app's notifications capability.

I use SMS Popup which lets you carry on using the built-in Messaging app to send and receive text messages, but replaces the notifications. Amongst the extra options it gives you are individual, per-contact customization of every aspect of the notification.