Let's focus on the issue...I JUST got a new SIM card, and I'm located in Taiwan.
1) Inserted SIM card for the first time, there's no problem there, got full coverage.
2) When I go into an elevator/basement where there is no coverage, iPhone4 is NOT able to relocate the sevice.
3) When I reboot my iPhone4, I get service back.
4) I used the SIM card on other phones and there is nothing wrong with the SIM card or how it is placed.
5) I am CERTAIN this problem cycles when I go into no service area like the basement or elevator.
I do not live in Taiwan, so I got a cheap 2G SIM card. From what I have experienced and read on the forum, I am leaning towards the theory on the Modem Firmware 04.11.08 bug (even though I have no technical data to back me up)...
It might help to know what kind of SIM cards you guys have, perhaps the "reset" solution only works for more advanced cards like 3G cards, while those with 2G cards are seeing this problem over and over again...
HOWEVER, the 2G SIM card I used in China worked flawlessly with the SAME iOS. Perhaps this varies on different carriers. I am tempted upgrade my calling plan to a 3G card...the customer service for my carrier kept hinting me to upgrade it after seeing my iPhone4, I'm not sure if she was just trying to sell me their product, or there has been a ton of complaints for 2G SIM card.