My iPhone 3G showed a cheery silver Apple icon this morning.
The same Apple icon it showed last night when I did a routine (hygienic) shutdown and restart. The phone was stuck on startup.
I rebooted and, after rather a long time, it restarted. I then tried running iSystemInfo, which crashed immediately.
A great way to start the day. I didn’t have time to mess around, so I mounted the phone in iTunes. There was 1.85GB free of 16GB, but I deleted a movie anyway to free up even extra space. I then did a shutdown/restart and iSystemInfo ran normally.
I’ve seen similar behavior in the past when OS X desktop runs out of swap file space. I’ve also seen some curious messages lately from Byline, complaining of a lack of memory.
It smells like a software/hardware problem – maybe something wrong with the file system or to the physical storage media.
I didn’t find much searching on “iPhone hangs startup”, but I eventually found the key search phrase “Silver Apple of Death” (SAD) or Apple Logo of Death (ALoDs) or White Apple Logo of Death (WALD) 
For example (I’ve rewritten the original post) :
You must restore your iPhone with iTunes ….
Reset it by holding home button until your phone is shut off.
Hold the Home button while you connect your iPhone to a computer running iTunes. Wait until your phone shows the connect USB to computer screen, then release the home button.
Choose restore as a new phone.
Search for restore mode for more details, this is a well know problem and have already been complained thousands times…
I’ve come across several explanations, including problems with “Springboard” on complex iPhones. I suspect there are multiple causes, and the Springboard bug may have been fixed in 3.0. In my case I’m hoping it’s a file system corruption problem or the solid state equivalent of “bad sectors”.
My phone is working for now, but I’ll put some time on my calendar to do a restore .
 We need some acronym consensus! Note these are of a family: BSOD – Blue Screen of Death (Windows), SPOD – Spinning Pizza of Death (OS X) and SBOD (Spinning Beachball of Death) (OS X – alt). Tradition favors a four letter acronym, all upper case. I’d say WALD or SALD.
 If the restore doesn’t work I might try a “wipe” – forcing the OS to write to all sectors and perhaps mark some as unusable.
 This is from Apple discussions. There are fewer of these than one would expect. That’s what you see when Apple is deleting posts. Just saying …
Update: If you search on the words in the various names of this syndrome one finds better posts, such as this one and this one. Most do very well with the restore mode, but in some cases the problem recurs and the phone has to be replaced. Looks like a combination of hardware and software. I’ve read recently that RAM and other memory defects are much more common than once thought, I suspect that in older phones this may be due to emerging memory hardware issues. Even then a restore might help, especially if the issue is bad storage that the OS can work around.
Update b: When got home I synced the phone. I ended up doing a wipe first (from iPhone:Settings:Reset). That took about 90 minutes. I then plugged it into iTunes and I was invited to restore from my last backup. After the initial restore you get to restore Applications and Music. With past restores I've had quite a bit of cleanup and credentials re-entry, but this one worked perfectly. Nice improvement, even though a complete restore takes hours.