The “hidden power” feature is a misstatement on several levels. Some phones (particularly Nokia) used to (maybe still do?) offer this as a feature on *some* phones. But what it actually does is simply set the phone for lower sound quality which saves battery juice. There is no “hidden reserve” built into phones. And actually the code is #4720#. (*33370# actually turns up sound quality/lowers battery life)

The trick for the serial # has worked on some phones- but is not a standard feature. Many newer phones have the # listed somewhere in the general settings. Many older phones had it in a sticker in the battery or sim card area and/or on a sticker with the owners manual. In some countries carriers WILL shut off the phone if stolen. Not in the US though. (although the carriers ARE creating databases to do this, largely because of the number of muggings for iphones )

800-free-411 does indeed work, (or used to- not sure if they still exist?). At least in the US/Canada. But if you have a prepaid phone the minutes will still be deducted, and contract phones the call will count towards your minute allotment.