On 29.09.2012, I bought an iPad 3 wifi+4g LTE model, 64 GB. I did an upgrade to IO6. I inserted a Vodafone 3G microsim into it. Initially everything was going right. But at home I used it over wifi. And after that my 3G connection is not working. Though in the status bar full strength is showing. Whenever I try to browse I get the message "Could not activate cellular data network. You are not subscribed to a cellular data service." I did on and off many times and even removed the sim and inserted it again but the problem is not resolved. Please help.

Same happend to me...no solution yet...

When you upgrade iOS, usually a carrier update is also applied. This can reset your APN settings. Which country's Vodafone are you on? Check with them for the correct APN settings for your account.

When I got my iPad, Vodafone AU gave me a card with the process to fix this APN setting any time a carrier update was performed. You may need something similar.