iMessage for android?

Hey all I got my Nexus 7 a few days ago to complemet my Galaxy Nexus , and so far there's only thing I miss from iPhone + iPad combo I used to have and that's iMessage. Now I know the fist thing people will tell me is that I can get that functionality from Google Voice, but I don't currently use that number, and would prefer not to have to switch numbers. So does any one know of an app I could use to send my text messages from my Nexus 7?