Almost all apps on the iPhone can easily open a URL in Safari. But normally you can’t open a URL from within Safari in other apps, for example in iCab Mobile (V 1.7).
Because you can’t create Bookmarks from scratch in Safari on the iPhone, you should just create a bookmark of a random page and change its URL to the above line and the title to “Open in iCab Mobile”.
If you open this bookmarklet from within the Safari bookmarks, the currently displayed web page is passed to iCab Mobile and opened there.
The bookmarklet simply changes the URL scheme from “http” to “web” and from “https” to “webs”. And because iCab Mobile supports the “web” and “webs” schemes as a replacement for “http” and “https”, the iPhone OS will pass these modified URLs to iCab Mobile.