It's not. Mine experienced this problem twice without jailbreak, both times on 5.0.
Now on 5.0.1 and jailbroken, this problem has not yet come back (finger crossed)

Untethered JB released? Feel like using JB to respring instead of having restart the non JB IOS5.01

My problem happens every time I go in / out the lift. Jeez...

Not released yet.
I'm using semi-tethered jailbreak.

I see. I got fed up on this prob and write to apple inc on this but no reply at all.

The best remedy I have tried so far is to use manual network selection as suggested.

(i) 3G on
(ii) imessage on
(iii) no jailbreak
(iv) iOS5.0.1
(v) Maxis
(vi) iPhone 4

With twice network lost for the day, but at least it can still rediscover the network.

If you can re-discover the network, then your iPhone is fine...
Our mentioned problem is once the network lost, will never able to find any network...
Need to restart only able to find network (but the same problem will occur again)

just wanna ask some question since i'm new in iphone...

i recently given an iphone3gs with ios4.1 installed and it was already jailbreak. i accidently upgrade to ios5, and later i cant even activate my phone. then i restore my phone back, hoping it will back to normal but it still ask me to activate it (which i failed to activate it again)

so any idea of what happening and what should i do? thanks

After restored to 5.0.1 like 5 days without problem...
This problem had once again come back...!
DAMN!!!

2 days n counting. hopefully it wont happen to mine that fast

Really super frustrating! Had to restore once a week?
Did Apple actually tested their iOS before launch?
First the battery issue (big issue), then now this no service issue
Don't tell me none of the testers did actually faced all these bugs
Really really really disappointed on this iOS 5!

Problem reoccured on the 3rd day (not counting those days where i switch off the phone for my trip). Reset network settings but no avail, a restart is needed. The problem manifested now is in the minor stage where a restart will solve things which will probably progress to the chronic stage where even the network is showing maxis, but the phone won't ring when people call in.

Probably gonna restore again when that happens, now to avoid lifts to prevent network lost.

Same here, the top-left corner shows network signal connected but it was fake.
Not able to make call/sms nor receive call/sms.
And yet the whole thing will just stuck there forever.
Now I'm restoring like once every 5 days to 1 week. Duh

I guess either restore back again or reset all settings. It should work if yours is unlocked set.

Sigh, its been ages, and apple has not responded. They only promise to fix the battery life issue in 5.0.2. sigh. waddafak!

No guessing. It doesnt work.

I actually install semi tethered right after I JB...but the no signal become worst...and no way to make any calls even with Signals. I dunno if this gotta do with semi tethered or not but after I did a restore, I didn't install it again.

Anyway, so far it's ok. Even after no signal at some areas it does search and pickup the telco. Can make calls also. Hope it remains ok

Restore works. But only works for few days and the problem will come back.

I can confirm that this No Service bug is not caused by jailbreak nor semi-tethered.
Because the first two times where I faced this problem my iPhone was not jailbroken.
And from my experience, after restore your phone will work flawlessly, but only for a few days before it comes back.

Phew..luckily i didnt upgrade my firmware to OS5..iam happy with my OS4 now..just thinking to upgrade it...but after read all the annoying issues of OS5...i wont dare to upgrade!

wow...there's alot of people facing the same problem? i though mine only..
everytime keluar lift, "no service" like forever until i restart the phone..

i'm on IOS5 also... grrrrr...damn annoying!!

Thx for the info. I will install semi tethered again. Kinda troublesome bringing my old HTC as backup.