As a starting point, Jeff recommends
Begin by studying various SAML Profiles, e.g. those given in [[SAMLProf]] and [SIP-SAML]. One will likely find the SAML Technical Overview whitepaper [[SAMLTechOvw]] helpful in this endeavor. It provides a detailed, illustrated expose of several of the SAML Web SSO profiles.Interestingly, when I view the document, a plugin Skype (yes Jeff, I know it's proprietary) installed when I recently upgraded renders a phone number in one of the XML examples as a 'click to call'.
Presents some intriguing possibilities for smart clients.