Sergey, you're not suggesting that you would be hacking into Delta wireless network while in flight?

If not, then you can run a network scan on subnet to identify available servers.  For example, if your assigned IP address is 192.168.12.35, then gateway most likely be 192.168.12.1 or 192.168.12.254.  You can manually ping each IP between 1 and 254 or have a software to do it.

Most likely once you get the gateway assigned, you will be able to browse to the "Delta Welcome to High-Speed Internet" page asking you to provide form of payment.

Was it an international flight?