The new iPhone version of ReQall puts a "related items" option on all entries. That option will link you to other ReQall entries as well as Evernote items that match up.
Items are linked by text. If you have a ReQall item that says, "Buy present for Joan," the related items you get will be those that have "Joan" in them or the word "present." And since Evernote recognizes text in photos you've stored on the service, you might find related pictures as well. If you have the Evernote app on your phone, when you click on the related item, ReQall will launch Evernote for that note.
You need a pro ReQall account, $24.99 a year, to use this feature.
I'm most interested in this addition since I'm a big Evernote user, and one of Evernote's biggest weaknesses is that it doesn't have a to-do list manager. This isn't quite that, but if you do use ReQall for to-dos, now they'll hook into related topic pages from Evernote.
The link will be available only in the mobile app for the time being; the ReQall Web service will get the link "soon," CEO Sunil Vemuri told me.