We have reviewed some of samsung mobile phones recently on out gadget blog www.getmeapp.com you can read the reviews here. One of the most common thing we have found in the android phones from samsung is that in some of the phones you might see the no signal or no network some times, it happens when there is low signal strength and the phone goes to airplane or offline mode automatically.
Normally, when the signal restores the phone should automatically show the network signal bars at the top right corner of the screen. Just in case if it does not then you can follow the procedure below by toggling the flight mode on the phone and then search for network manually and then select the network on the phone.
Just when you see no signal on your phone, go to Settings >> Wireless & Mobile Networks and Toggle airplane on and then put it to off.
Once you put the airplane mode to off, the phone should now catch the network signal it still it does not then go to Mobile Networks and search for network operator manually.
and then select your operator from the list.
The problem should be solved by following the procedure below, if still it does not leave a comment below and try to contact samsung care if the phone is in warranty.