Because the bombs aren't in phone form-factor, they're big vests packed with nails and shit, just set off by phones. People tend to notice when you walk into t

Because the bombs aren't in phone form-factor, they're big vests packed with nails and shit, just set off by phones. People tend to notice when you walk into the middle of a crowd, drop a large bag, then walk away. Now, in situations where they can pull that off, say crowded busses..., I'm sure they employ that tactic. Also, I imagine there is a heavier emotional impact associated with 'suicide' bombings.