Hello my fellow iPhone 4s users...
i have been going around the web for solution to the lost signal. Upon further investigation and diagnosis with my iPhone and other iPhone with a combination of chnage of sim between phones, resetting the network, hard reset and restoring a few times, it still persist. My analysis is that the iOS 5 >Settings>General>Cellular Data is the culprit. It does not have an option of switching between Edge and 3G (unlike the previous iOS lower than 5.0 or 5.0.1) It always stays on 3G. Now comes the trickiest part of my analysis. For networks having mid to low signal in areas, the updated dual antenna of the iPhone 4s switches automatically between 3G and normal signal. However, since it has no option to go down to Edge, it "automatically revert back to the original signal status". Sometimes from a very strong signal to a low signal area, it shows full bar of signal. but when you try to send an sms or make a call, it fails.
Conclusion:
I believe Apple has been digging deep with their softwate developers and checking the hardware of the iPhone 4s. And if my analysis is correct, they may have to incorporate the option of EDGE and 3G again.
Temporary Solution:
For low reception/signal areas, actually NONE... we have to wait for the update by Apple.
So either use our iPhone 4s as an expensive iPod on poor reception/signal areas and transfer our sim cards temporarily to another phone or have your phone put to AIRPLANE MODE on-off again.