Thanks Carlos. But to clarify my question: There is clearly is *some* kind of standard out there, as indicated by the number of (big) vendors who implement it in an agreed-upon way. So, what I'm trying to figure out is what that standard is and where it's defined. The Neustar documentation contains obvious cut-and-paste from an ABNF spec: calling-name-request = callee CRLF [ called CRLF ] callee =?Calling-Party? HCOLON addr-spec called =?Called-Party? HCOLON addr-spec addr-spec =SIP URI / SIPS URI / TEL URI And it does not seem thematically consistent with the general tenor of that document to suddenly break out some ABNF on their own accord. So, this syntax spec comes from *somewhere*, though no citations revealing its provenance are provided. The same kind of thing is true in all other docs on this topic from other major vendors. None of them reference anything non-generic (e.g. RFC 3265). So, what's the standard? Is it the Verizon patent? If so, why don't they any vendor docs refer to it by name? -- Alex -- Alex Balashov | Principal | Evariste Systems LLC Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/