Devilwoman, there are too many variables for a definitive answer to you question. Where in the States, what time of the day are you calling, what system are you with etc...
there is a website called telestont, it will give you a number to call before dialling the number you want. it will cost you 2p per minute to call anywhere abroad from any network here.
yes it is only 2p per min. i use it to call my friend in Australia and my brother in China. Call it and it should say ' calls cost 2p per minute'. Do it from a UK landline.
Planet Talk does the same sort of thing. I save a fortune as i phone Spain a couple of times a week. �20 credit lasts me about 6-8 months. Look at their website