There's a long list of things we love to blame for poor wireless signals—the weather, antenna placement, AT&T—and insulation is rarely one of them. It should be, though, because the insulation in your walls at home and at the office could be the real reason you're dropping calls.
Some construction materials are well-known to mess around with wireless signal strength. You don't have to guess that you'll drop to one bar walking inside of an old concrete building, for example. But even lighter modern structures will give you trouble if they're cushioned with foil-backed insulation, as we recently learned from a friend who works for AT&T.
Some solid foam and fiberglass insulation, the stuff inside of roofs and exterior walls that shields your home from the elements, has foil backing. The foil does a little bit to help reflect heat, but it does a lot to effectively kill the transmittance of cellular or wifi signals throughout your home. It can even block signals between adjacent rooms.
If you're sketching out a renovation or a new build, consider non-foil insulation to boost signal strength in your space. If you can't or don't want to send foil-backs packing, signal amplifying devices like AT&T's Microcell 3G or Verizon Wireless' 3G Network Extender will help boost your bars in the meantime.