I have Galaxy S and I was using old 2G card for a year. Updated card to 4G in July, and worked well. Then I went to vacaton to Europe and used there some other SIM card in my phone without any issues.
On the way back, in the plane, I first turned on flight mode (it was still EU SIM card there), but soon gave up of using the phone in the plain.
The next time I turned the phone on in USA I put our T-mobile SIM card and my phone did no recoginzed it. It was replying with a message that SIM card is not installed, even it was there in SIM card slot, properly settled.
Then, I took out my card and put in my husbands T-mobile card, and the phone behaved exactly the same: SIM card was not recognized by it.
My husbands SIM card works on his phone (Samsung Sidekick) and I tried my card on my old blackberry and it works.
I tried again to install my SIM card on Galaxy, but no success. I also return all settings to a factory settings and also formatted Galaxy phoen again, but in vain. In spite everything else is working normaly on the phone, there is no bars - SIM card is not red by phone.