It's almost certainly a suicide bombing. The only question is whether there is an identifiable motive. Was there a target? Was the motive purely personal? As in, "I hate the world because I have no friends and my wife left me." or is it, "Somebody had to take this war directly to AT&T, to punish them for their role in the War on Christmas!"
If he just wanted to kill himself, there are easier ways to do it that don't require such elaborate preparations, and won't damage property or risk injury or death to others. He clearly wanted to do something that had some other effect that ending his own miserable existence, but what? So far, there are no clues available to those of us who depend on publicly released information.
The warning announcement is one that doesn't seem to have any similarity with previous terrorist incidents, so it's hard to find an analogous situation.