Help ! Auto authentication in Wi-Fi by special SIM with prepaid authorization. How ?

Hello, collegues !
I must confess I do not have iPAD and I use tabs under Android. But. But I plan to buy it to keep you a company.
Could anybody from iPAD owners please to explain me the algorithm of automatic authentication in Wi-Fi by using of SIM with prepaid authorization for that ?
In Russia where I live, Cellular provider Beeline offers a special tarif for iPAD with such a possibility (mobile Internet plus free access to its Wi-Fi spots and zones. So I do want to understand how does it work.

Thanks in advance.

Best regards,

Jimmy