A hip and latest word of today's "I'm gonna be"...OR
"I'm going to be"...OR "I may be"...
Hence, it's a shortcut, specially used in Instant Messaging, texting and/or eMailing in order to conserve a long sentence thus saving time specially for those who are non-typists.
Immabe in the store at that time.
Immabe busy tomorrow.
Immabe looking for a job.