vodafone subscriptions have a public ip address by default. If you have a monthly fee internet, the default APN is standardnet.vodafone.net, which in principle gives you a public address, but if that doesn't work, use the internet.vodafone.net APN. For a top-up card, you can use vitamax.internet.vodafone.net or vitamax.snet.vodafone.net APNs. You can read more useful information HERE.