It runs fine on the ATT IPhone4. I have maybe 4 or 5 apps out of about 50 that don't work but nothing major that I can't do without for a while. The push mail stops working off and on and I can't figure out why. It works for a while and then stops. Deleting the email account and adding it back fixes it or even just turning the device off and then back on also fixes it. Overall, for an early beta it runs surprisingly well. I am enjoying it.