Quick back story before someone tells me to buy an app. =)
I just got an EVO and it chews through the battery fairly quick. I downloaded JuiceDefender to manage
final ConnectivityManager conman = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
final Class conmanClass = Class.forName(conman.getClass().getName());
final Field connectivityManagerField = conmanClass.getDeclaredField("mService");
connectivityManagerField.setAccessible(true);
final Object connectivityManager = connectivityManagerField.get(conman);
final Class connectivityManagerClass = Class.forName(connectivityManager.getClass().getName());
final Method setMobileDataEnabledMethod = connectivityManagerClass.getDeclaredMethod("setMobileDataEnabled", Boolean.TYPE);
setMobileDataEnabledMethod.setAccessible(true);
setMobileDataEnabledMethod.invoke(connectivityManager, enabled); // pass true or false