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It means that there is no network coverage in your area. In most cases, your operator or service provider is the best source of assistance with issues regarding network coverage.
When you are in outdoors, move your position to find a good signal network coverage area.
When you are in indoors ( like building, basement and subway station), change your position by small spaces, or move towards a window.
If other mobile phones with the same operator or service provider as yours does not have a signal
too, then it is conclusive that there is no network coverage.
If other mobile phones with the same operator or service provider as yours does have a signa
l, then you need to upgrade your cell phones firmware. Unfortunately, there is no upgrade available from Samsung's Website http://www.samsung.com/in/consumer/mobile-phone/mobile-phone/cdma-phone/SCH-B209ZKAREL/index.idx?pagetype=prd_detail&tab=support
Samsung B209 uses CDMA Technology at 800Mhz frequency. If your operator or provider uses GSM Technology, then your phone will not get any signal.
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Have a great day.