SGH-D900 "No service" message even though signal bar shows reception

Hey all, this is my first post here, so please bear with my newbie mistakes and incorrect technical terms.

I´m in desperate need of help because my Samsung D900 stopped working with my service provider all of a sudden.

A little background: I live in Brazil, my service provider (TIM) uses GSM network.

So I bought this brand new unlocked cell phone 6 months ago, and it has always worked perfectly with my service provider. About two weeks all of a sudden the phone started displaying either the message "no service" or "searching" even though I was in locations where I knew I had strong signals and other phones using the same provider were working perfectly. My signal bar displays maximum reception but I stil get the "no service" message on the LCD and I cannot place or receive any calls. The wierdest thing is that the phone will work with other SIM cards from other GSM providers form my country. It just stopped working out of the blue with mine (TIM)!

I have contacted TIM and after changing a bunch of network settings on the phone (which did no good at all) they told me that the problem wasn´t on their end, that I had to look for a Samsung service center to fix this. I went to Samsung and they guaranteed me that the problem was with TIM´s network since they tested the phone with other SIM cards from other providers and it worked.

So it boils down to this: the phone won´t work specifically with this network. I have tested other SIM cards from TIM and it still won´t work. I have tried to manually change all network settings on the phone and I have tried reseting it.

Can anyone please help? This has been going on for almost a month and I need this phone working! thank you very much for your help people.

Best regards,
Victor

I have been experiencing the exact same set of issues with my Samsung D900 which I purchased back in February of 07. Oddly enough when I use several of my friends T-Mobile sim cards, the phone doesn’t seem to have any problems at all

Even though people right next to me who have other AT&T cell phones have all five bars of signal. I have all five signal bars or even no bars at all displaying a "No Service" or "Searching" for signal message, this is very strange knowing that im in an area with good reception. On top of all this, my calls have also been dropping intermittently or not going through at all. All of these problems started about 3-4 months ago.

It's very ironic to have a network such as AT&T which advertises the fewest dropped calls in the country then only to have your calls dropped repeatedly.

I live in Alexandria, Virginia, USA and use the AT&T Network.