iPhone 4s, 16G, noverlock, my friend bought for me from Canadian online store. I got the phone in Hillsboro, US where we met on business purpose. I put my native (MTS-Armenia) SIM card which has roaming enabled, connected to ATT network and never lost network during 7 days I was on my trip to US (stayed 2 days in LA area as well). The phone originally came with iOS 5.0.0 (modem firm. 01.00.11).
When I came back home Armenia phone was not loosing network for a day, then iOS 5.0.1 (modem firm. 01.00.13) update automatically downloaded and I agreed to install. Next day no-service, invalid-sim, sim-failure, no-sim... Interesting thing is that even on times when network showed connected, calls fail, no data connection available, and my number was not reachable for calls. Also if you try making service command requests (e.g. *315# for bill info) - phone hangs at all, you can only turn it off then on to bring it back to work.
I've bought sim from other local provider, Orange-Armenia (officially selling iPhones), cut the card, put in the phone - no network issues at all for 2 days. The other SIM card not working in iPhone 4s, is perfectly working in my iPhone 4 for 2 years and now on...
I would like also to mention that per my observations, battery of iPhone 4s with Orange-Armeni is NOT dying to fast.
Apple changes modem hardware with iPhone 4s, but seems they did not programm a good firmware for it yet. It works just fine on one operator network (Orange in Armenia has latest/best-in-class hardware installed) and does not work at all on other...
One thing I cannot understand, why SIM card replacement is hepfull for ATT people in US... Unless SIM cards coming with ATT package are broken or something like that. But in that case they shouldn't work at all instead of working a day or an hour then not work and then work after reboot...although if something is wrong with the voltage settgings, it will become unstable and unpredictable.
If Aplle installed modem hardware which doesn not support some types of SIM cards, or some network equipment - then they must report that. If it can be fixed by modem firmware, then they have to hurry. Otherwise they cell phones to meet their corporate plans, but they will fail because people can sue them...
p.s. Steve - RIP, but I'm afraid Apple won't be so good in meeting customer needs without you...