55cents per minute. BUT... depends on what plan you are running with.
If you have any of the recent plans. you can get a value pack for 6.99 and it gives you preferred rates for US at 10 cents per minute which is much cheaper. (if you already have a value pack, 4.99 its just 2 dollars more, so not that bad as it gets replaced)
4.99 Value Pack Includes: Name Display Enhanced Voicemail Who Called
4.99 Value Pack Includes: Name Display Enhanced Voicemail Who Called US & International Unlimited SMS US & International Preferred Rates
Hope this helps, what plan do you have currently, older plans had different rates but above is the most common information.
Edit: Also $5 you can get an add-on just to have preferred rates US & Internationally.