Also applies to iPad
It is possible to download a wiki so that you can use it when you are not connected to the internet. The wiki is sent to you attached to an e-mail as a .zip file containing each page as a separate .html file. To view these on your iPhone you first need to copy them from your desktop PC or Mac onto your iPhone. As there is no builtin mechanism on the iPhone to do this, you'll need to use an App such as Files, Files2, or any of a number of similar apps that are available.