I would be very surprised to learn that the iPhone has monitor mode capable drivers that would allow the requisite packet capturing for aircrack-ng.
As for WPA, that is extremely processor intensive, as the same pass phrase on a different AP with a different SSID will yield different encryption keys - so essentially it's a dictionary attack on the SSID hoping to yield the passphrase. I doubt the battery would last even if the processor is up to the challenge.
