If it says specific carrier then it can only be activated with those carriers. Do not assume that it will work with your carrier unless stated.
The item "New Open Box Samsung Galaxy S8 G950U G950U1 Black GSM Unlocked AT&T T-Mobile" is in sale since Friday, May 18, 2018. This item is in the category "Cell Phones & Accessories\Cell Phones & Smartphones". The seller is "mobile-us" and is located in Northbrook, Illinois. This item can be shipped to United States, Canada, United Kingdom, Denmark, Romania, Slovakia, Bulgaria, Czech republic, Finland, Hungary, Latvia, Lithuania, Malta, Estonia, Australia, Greece, Portugal, Cyprus, Slovenia, Japan, China, Sweden, South Korea, Taiwan, Belgium, France, Ireland, Netherlands, Poland, Spain, Italy, Germany, Austria, Bahamas, Israel, Mexico, New Zealand, Singapore, Switzerland, Norway, United arab emirates, Qatar, Kuwait, Bahrain, Croatia, Costa rica, Antigua and barbuda, Aruba, Belize, Dominica, Grenada, Saint kitts and nevis, Saint lucia, Montserrat, Turks and caicos islands, Barbados, Bermuda, Brunei darussalam, Bolivia, French guiana, Guernsey, Gibraltar, Guadeloupe, Iceland, Jersey, Jordan, Cambodia, Cayman islands, Liechtenstein, Sri lanka, Luxembourg, Monaco, Macao, Martinique, Maldives, Oman, Pakistan, Paraguay, Reunion, Uruguay, South africa.