Salesforce.com will say on Wednesday that it has bought instranet, a company that makes technology for customer service, for $31.5 million. This is its biggest purchase to date.

With the purchase, the company known for its burgundy “no software” logo, which helped start the software-as-a-service era, actually gets a software company. Even though Salesforce.com plans to create a SaaS copy, InStranet’s software is already running on-premises at customers like Comcast and Expedia. Brett Queener, Salesforce’s senior Manager of apps, said that Salesforce will continue to assist and sell on-premises implementations.

But don’t think that Salesforce is going in a different direction, Queener said. Aside from on-premises implementations, Salesforce wanted the business’s technical architecture and features because they fill a gap in Salesforce’s own CRM offerings, said Queener.

InStranet makes a website that helps customers at conscious Web portals and customer-service agencies get better and faster responses to their inquiries and problems. The software was made by InStranet, which was started in 1999 by Alex Dayon & Jean-Noel Grandval, two former Financial Objects executives. The software is based on the use of multiple data cubes.

InStranet puts information about customers into groups based on things like where they live and what products they’ve bought. So, if a customer of a telecommunications company looks for help with a problem on the self-service site, for example, InStranet makes it more likely that the site will give answers that are relevant to the customer’s situation.

Before it was bought out on August 4, VimpelCom, France Telephone service, 3M, and Manpower were also purchasers of InStranet, which was privately owned. InformationWeek has put out a detailed report and survey to learn more about companies like this one that is using SaaS. Here you can get the report (registration required).

Call-center workers likewise employ the software to find answers for customers more quickly. Smaller deployments by InStranet have only taken a few weeks, while Comcast’s enlistment of 20,000 customer service agents got about three months. Salesforce says that about 350,000 customer service reps at many different companies use the instranet. Most of InStranet’s activities are in Paris, but so far its headquarters are located in Chicago.

In 2006, Salesforce.com paid $15 million to buy the wireless infrastructure company India. This purchase is more than double that amount.

Also on Wednesday, after the stock market closes, Salesforce.com will report its earnings for the fiscal quarter that ended on July 31.