The most direct route between a smart phone and the micro controller world of sensor appears to be bluetooth.  This wireless technology has been around for some time now.  The hard work has been done and the road has been laid out.

Control your Arduino board from your Android device over Bluetooth, here’s a demo.  How easy is that!

The adapters are simple and inexpensive.  The smart phones have bluetooth support.  It just makes sense.  I was able to find two sources for adapters, Vetco sells a simple adapter, as does Ada Fruit.

But the real benefit is getting what you want done, and since Spring Break is at the door, I suggest that everyone enjoy the benefits of thier hard work.