If you are inside a thread, there's a menu-like thing above the first post saying << Page XX >> or smoething similar. You can click Page XX and then a small menu will open and you can choose to go to any page.
I have to say this link layout for pagination is nearly impossible to use from an iPhone or similar touch-screen device.
First, the links are often single digits, very hard to accurately press.
Second, the surrounding background is also hyperlinked; essentially every pixel on the screen is some form of hyperlink. Even with a proper mouse the pagination is difficult to use.
Yeah, it's pretty difficult to use this forum on an iPhone. You have to zoom in on the page numbers so that they are easier to click on. I bookmarked the "20 recent posts" page, but of course it lists them recent to oldest which means you have scroll down to bottom.
Writing a message is not easy either because the keyboard takes up too much of the screen, leaving only enough space for 3 lines of text.
Still, the iPhone has the best web browser of any phone I've seen so far.