[Ken Case]

You can drag contacts from AddressBook, calendar appointments from iCal, web pages from a browser, files from Finder, or (with Option held down) tasks from OmniFocus onto a task to add a link back to the dragged item.

However, those links won't be supported on the phone in version 1.0. What will be supported in this first release is automatic recognition of phone numbers and URLs, so "206-555-1234" and "http://www.omnigroup.com/" will both turn into clickable links.

P.S. — Going the other way on the desktop, you can also drag tasks from OmniFocus into other applications which accept URL drags (such as OmniOutliner).