Why does a Double Hard Reset help with iPhone issues? My wife has an iPhone 3G, me an iPhone 4.

Ever since she upgraded to iOS 4, her phone has been much slower than it was on iOS 3.

My iPhone 4, upon upgrading to iOS 5, isn’t slower. However it has greatly reduced battery life and gets physically warm for seemingly no reason.

What do these two things have in common (besides being upgraded to a firmware designed for the next generation of hardware)?

Both phones can be temporarily healed of their maladies by being Double Hard Reset.

According to Cult of Mac:


  To perform a Hard Reset, press and hold the Home and Sleep/Wake
  buttons on your iPhone simultaneously for 5 to 10 seconds.  After a
  few seconds the Slide to Power Off notice will appear, ignore this and
  keep holding down both buttons. In another few seconds the device
  should abruptly turn off.


They go on to say that the device will reboot itself after you've done this, but both of my devices stay off.

To complete the “Double Hard Reset,” you need to power on the phone after you’ve done this, then do it again before the phone gets to your lock screen.

I have personally experienced this numerous times.

Why does this help?  What does doing a Double Hard Reset do to the phones?
It sounds like you’re no doing the reset correctly. You’re supposed to keep holding the Home and Sleep buttons until the Apple logo appears.

The reason your iPhone isn’t coming back up is you’re stopping before the reset is completed.