For learning purposes i want to play around with a sound meter. Are the smartphone sound meter apps (have a droid 2) that accurate? Is a $30 hand held sound meter usually going to be more accurate?
The key difference is calibration: a hand held sound meter, even a cheap one, has been calibrated in the factory. Your app and phone (microphone, internal preamp, dac) aren't. If you find a way to calibrate your app - most apps have a calibration setting - using a reference sound source or a calibrated SPL meter, you can improve the usefulness of those apps.
Both a cheap meter and a calibrated app will not be 100% accurate, so take the readings with an uncertainty of at least ± 1 dB, and increase that uncertainty for very high or very low frequencies.