What gives AT&T? I'm staring at a tower, have full signal, and still can't make a call?

Now I understand that there are times when any technology will have problems, but seriously?  AT&T, I was driving by, staring at a cell tower with full signal on my phone, and I couldn't complete a call?  I tried two different numbers five different times and finally got my Verizon phone to make the call...

AT&T, Less bars in More Places!