Can phone signals penetrate glass, so can I expect phone signals to come if I am sitting inside a closed AC car.
I assume you mean an Air Conditioned (AC) car with the windows rolled up.
Yes, your cell phone will work wonderfully inside your car.
Cell phone signals are electromagnetic (E-M) waves, just like light; but the cell phone E-M waves are longer than the E-M waves which make up visible light. The reason we see differnt colors is that objects reflect and absorb light based on the material's interaction with different wavelengths of light. For instance, you see a blue object, because it absorbs all other colors, but reflects blue. Glass is transparent because is doesn't reflect or absorb any visible color. You can think of E-M waves outside the visible spectrum as 'colors' of light which we can't see. It just so happens that glass doesn't significantly reflect or absorb the 'color' of E-M waves that cell phones use (neither does wood, brick, drywall, and most other non-metallic substances).
This seems like a situation tailor-made for an experiment! Get in your car, close the windows, and call someone.
But anyway, the answer is yes, these signals do pass through glass, as well as other solid materials: you can get mobile phone calls in your home, for instance, even if you're not near a window.