There r two points on the the phone.. The top left corner near the earphone jack and the bottom left corner.. If u touch them both with one hand.. U can c da signal bars decreasing very slowly..
I've tried making calls even after the bars r down and the calls go through with no prob..
The bumper cover is not only available at apple stores .. Now the mobile accessory manufacturers r making better looking and quality stuff..
If u still not buying thinking if the prob.. Don't worry abt nothing..
It's really worth buying.