Try this:
Cursor c = contentResolver.query(CallLog.Calls.CONTENT_URI,
new String[] { CallLog.Calls.DATE, CallLog.Calls.DURATION,
CallLog.Calls.NUMBER, CallLog.Calls._ID },
CallLog.Calls.DATE + ">?",
new String[] { String.valueOf(sinceDate.getTime())},
CallLog.Calls.NUMBER + " asc");
sinceDate
is a Date variable that is set to the beginning of the period you will want to cover.