I recently had a friend text me "ima go to [the local pub]. U in?" I [understood it](http://www.urbandictionary.com/define.php?term=ima) just fine as meaning "I'm going to", but being an old fogey, I'm not sure if this is just txtspk or if *ima* is something people actually say.

Is this just a texting abbreviation? If people really say this, how common is it and where is it mostly used? For instance, can I say it at the office, like "Ima get the spec to you by Thursday." Or is it more casual than that?