To Announce Cross-Company Instant Messaging For Chatter will announce new features for its “Facebook for enterprise” service Chatter this week at its annual Dreamforce conference. CEO Marc Benioff already revealed during his TechCrunch Disrupt fireside chat that the company is adding a Box/Dropbox-style file-sharing system called ChatterBox. Now I’m hearing from multiple sources that Chatter will also be getting secure cross-company instant messaging.

Chatter already has an instant messaging feature, but it only works with people within your company. If you have suppliers or partners you need to chat with you’ll need an external application. The idea is to enable companies to collaborate with people outside its own corporate firewall, and it’s something has been talking about since instant messaging was announced in May.

This fits with the ChatterBox idea. One of the selling points of tools like Dropbox is that you can share large files with people outside your corporate network. Huddle, another service in this market, has made external collaboration a central selling point. Having a secure enterprise instant messaging system from cross-company communication, instead of relying on free consumer tools like Gtalk and Skype, makes a lot of sense.

So much sense that is nowhere near the first company to think of it. Chatter’s instant messaging features will compete with similar products like HipChat (which was acquired by Atlassian in March), Campfire (a service from 37signals) and Grove (an enterprise chat tool based on IRC).

One potential upside for companies already using Chatter is that they might be able to consolidate instant messaging into one application. That is, if they can get everyone they need to chat with to use Chatter, too. Otherwise it will be yet another communications tool to add to the stack.

Besides ChatterBox and the new instant messaging features, is expected to unveil (which is probably based on its Rypple and ChoicePass acquisitions) and a single sign-on service similar to Okta (a company that just happens to be founded by former VP of engineering Todd McKinnon).

Also be on the lookout for information on how its GoInstant, Thinkfuse and Stypi acquisitions will factor into the the company’s strategy.