Not AT&T customers pay 3.99 USD per a session when they connect PCs to AT&T wifi. But the pages of URLs are not easy to understand. That is why I asked this question. Certainly, the Gophone smartphone plans page mentions Wifi(But 30 USD montly plan only. )
http://www.att.com/shop/wireless/plans/prepaidplans.html
Then, this page :http://www.att.com/att/gophone-tablet/en/index.html doensn't mention AT&T wifi basic.