I don't use any kind of IM anymore except gtalk every once in a while but I know back when I used a winmo phone almost all the im clients sent and received via sms except one called palringo, looks like its available on android too.
One neat thing about it (on winmo at least, I'd assume the android one has this and more) was that you could insert still pictures from the camera realtime into a chat, it had a button take a picture when you clicked, it immediately uploaded the jpg to palringos servers and sent an http link to the pic to your recipient.
Also I don't know how it works now but back then at least, palringo did not connect directly to yahoo/live/aim/etc servers. Your phone had an ip connection to palringos servers and they had a connection to yahoo or whatever. Just FYI your stuff may be going through a 3rd party system.