I recently upgraded my iPhone to iOS 4 and like many others I noticed that everything slowed WAY down.  luckily I ran across an articled called Speed Up iPhone 3G + iOS4 with a Hard Reset? which gave some very good advice.  Basically the fix calls for  a double Hard Reset.

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, followed by the Apple logo and a reboot. Now release the buttons.

If your iPhone remains powered off, wait about 15 seconds then boot the phone by pressing theSleep/Wake button.

The tip mentions that it may be necessary to perform the Hard Reset twice to get the desired effect.  I tried this on my iPhone 3G. I performed one reset and it rebooted immediately.  Before repeating I checked to see if I could notice any difference: maybe, not much, kinda hard to say.

I then did a second Hard Reset and this time my phone stayed off.  Rebooted again, and was happy to find that yes, my iPhone does seem to be peppier – or rather, back to it’s normal pokey nature instead of incredibly sluggish.  Apps load faster, Mail messages open quicker – yay!

A bit of Googling yields little information as to what exactly gets reset during this operation.  What I found just notes that the iPhone is a computer like any other, and a hard reset typically clears all RAM buffers, caches, etc.  That can indeed help with performance.

Worth a shot.  If this helps – or doesn’t – with your iPhone, let us know in the comments.

Based on user feedback the Double Hard Reset (“DHR”) does appear to help a large number of 3G owners.

For more tips see our followup post iPhone 3G Performance Suffering with iOS4.