We are thinking about upgrading to SBS 2011. We would also like a way to collaborate with our external clients using Sharepoint Foundation, which is built into SBS 2011. Is this possible? I know in full Sharepoint you can publish client facing sites where you can share documents back and forth, but I wasn't sure if Sharepoint Foundation could do this.
The technology supports it but the SharePoint Foundation License does not. In order to set up this type of scenario you would need a license for SharePoint Server 2010 for Internet Sites.
Check out Microsoft's SharePoint Licensing Q&A for more details.