Licensing Model in SharePoint
There has been lot of confusion on the licensing information in SharePoint like what comes free, what is the licensed part of the product, what are the various client access license (CALs) options available. The following diagram helps clarify most of the doubts one will have around this.
Source: Microsoft Documentation
The bottom layer shows the features available with WSS 3.0 which comes free of cost. The intermediate layer shows the features of MOSS available with Basic Client Access License (CAL). Most of the content management is possible with the basic client access license (CAL). However to leverage other services like that of accessing line of business application data, Excel Services or Form Services for viewing Infopath Forms through Browser, Additional Client Access Licenses will be required which is shown as the top most layer in the figure.
Note: In case of Internet Portals there is no concept of CALs and the licensing cost for MOSS is close to 8 folds the cost of MOSS server product.