Skype allows to call 800 phones in the US for free.
Free Google 411 directory assistance service allowed you to call free of charge. Just install Skype and dial 800-FREE411 (800-373-3411) for free. Since US 800 calls made with Skype are free, you won't pay a penny for the service.
Note that Google uses Speech Recognition, so you will need to speak English. You will need to tell the speech recognition directory assistance the city/town of the person/business you are trying to reach and then it will connect the call for you - FREE of charge!
Of course this trick only works if the person you are calling is in the directory (not unpublished number).
Note that you have to listen to an ad before the call is connected.