Share your experience!
When I've bought my Xperia S, I've noticed, that sometimes my phone signal is gone. First I thought, that it's network provider's problem, but after a while, I've noticed, that my parents and sister (they are using the same network provider) don't have that problem. The signal comes back only when I restart my phone. It really annoys me, because I can't get any messages or calls ant it drains my battery faster.
I've tried to reinstall my phohe using PCC, but it didn't solve the problem.
Phone info.
Any suggestions? This morning it happened again..
Anyone? I thought flagship devices had better support.
My bad. 
well i'm not an expert but i'll tell you my suggestions
1- Do a factory reset
2- Repair using Sony update service not Pc Companion
3- Do another factory reset
if that didn't help try to use a new simcard
1. Didn't help
2. Already tried.
3. It happens with any simcard.
Thanks for suggestions. 
Well, I guess I'll have to wait for the Jelly Bean update and hope, that it will fix this problem. 
I suggest that you have your phone examined and fixed at an repair center if this happens using any SIM card. Contact your local support team for more info.
http://www.sonymobile.com/global-en/support/contact-us/contact-info/
So, finally I have received Jelly Bean update and guess what I have found this morning. No Service. 
Had to reboot my phone again. My SIM is new and signal on other phones is great.
Android version: 4.1.2 Jelly Bean
Build number: 6.2.B.0.200
Ever since I updated to Jelly bean, the phone loses signal, it's like the antenna stops working all of a sudden. Doesn't seem to be a hardware issue as it didn't occur while the phone was on ICS...
That is not encouraging news. The only reason I wanted JB was to fix the periodic loss of network.