My iphone wont pick up a signal.

I bought my iphone 3 days ago, and i can hardly get a signal. It just keeps on "searching.." which is draining the life out of my battery.
i have restored my iphone, changed the simcard, reset the network settings several time.. and nothing.
I have made an appointment at the apple store, but can't get in for another 3 days.
so at the moment its just like a fat ipod. 😐
has anyone else had this problem with their iphone?