Hello, my apologies if this has already been posted before or similar..... I am considering to get an iphone 3g from ebay. The majority of the items i am interested in are unlocked. They are assigned to either At&t or O2 (uk) networks. Now, i have little knowledge about how to unlock an iphone in order so that i can use the phone on my contract network, which is Vodafone (uk). I have noticed that there are a few options about how to do this: Using a jailbraker program or using an add-on sim card. Now, do you need to obtain both of these to have the phone work on all networks or do you need to do just one? What does jailbrake actually do to the phone? Lastly, when you actually have enabled the iphone to work on all networks does the 3g internet function on a network other than the one the phone was originally assigned to (in my case Vodafone UK)? Hope you can help.