I am having the same problem. I dont know why this is happening some poeple think thats it because of the latest update but i am not sure. I am really upset because I use the internet on my iphone 4s alot because i have unlimited. But now it keeps on saying could not activate cellular data network. When i called virgin mobile customer service on a family members phone, they tried to help me but i have gotten disconnected around 4 times. It's very frustrating. They have told me to try and call ##873283# but when it starts the service update it fails. If you try it, maybe you are lucky and get the service update failed.