Have you checked the settings (settings -> internet connections -> connections, then select your vodafone connection, then edit -> next). Check your access point name (mine is "Internet", if yours is different, make sure it is set to what you expect). Then check user & p/w (both should be "web" for the "internet" AP).

Even if these settings look ok, it may be worth re-entering & saving?

Also worrh checking that the advanced tab has nothing funny in the proxies or IP address setup (unless you've intentionally modded these for some good reason).