How to tell if my iphone 4 has a signal problem?

I just got the iphone 4 for christmas and when i'm holding it sometimes the signal drops from 4 bars to 3 bars. Is this normal? Or have i got a defective phone? Sometimes it says searching aswell! If it is defective, what can i do about it? It the white 8gb model, running ios 6.0.1! Thanks for the help.

Added (1). Sometimes it can drop two bars! Even if i'm not moving anywhere!

Added (2). This is when i'm in my house! And i live in the city! Also if i have it in a case i always get a 5 bar signal!

Yeah if its like a one bar drop signals can change with one step now and again

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