Parameters: ios 4.1; Apple iPhone4 - 32Gb; Telus customer from BC; Currently in Santa Barbara, CA
Observed: No phone service at all (three days). "NO SERVICE" seen in upper left corner of iPhone screen..
Battery draining rapidly, necessitating more frequent re-charging for the past month.
Area where battery is located has been heating up noticeably.
What appears to fix my "NO SERVICE" problem is using the iTunes software on my laptop.
I updated the computer's iTunes software to the latest version.
I connected my iPhone to the laptop with the USB cable. iTunes started up and synched my phone, as usual.
Then, I backed up my phone: Manually backup and restore > Back Up Now
Then - I restored my backup: Manually backup and restore > Restore Backup
When this process was completed (one minute or so) the phone re-started
Now I see I have connectivity with AT&T. All bars visible. Problem went away .... Texts started coming in.