AT&T No Service After Updating iPhone Software During Latest Sync

After the Apple iPhone update, some iPhones may not recognize the AT&T network and persistently display “NO SERVICE” in the upper left corner of your iPhone display.

If your iPhone does not connect to the AT&T network after updating to version 1.01, try rebooting the iPhone by simultaneously pressing the iPhone Home Button (bottom/center below display) and the Sleep/Wake Button (top/right button when facing iPhone with Home Button at the bottom). You should see a silvery-white Apple logo on the display if the iPhone is rebooting.

iPhone update 1.0.1 is now available through iTunes. The new release patches several security flaws related to Safari, WebKit and WebCore.

Official docs from Apple …
Apple iPhone User’s Guide includes diagram of buttons and definitions
About the security content of iPhone v1.01 Update