[Serusers] Call limiting ?

Hi! As far as I know, SER does not have functionality of limiting number of calls on per-user basis. It was discussed years ago, and the reason for that was "We don't have ability to know is call still alive" (http://lists.iptel.org/pipermail/serusers/2004-November/013035.html) But, in April 2005, RFC 4028 (Session Timers in SIP) appeared, and it (at least theoretically) can be utilised to achieve knowlege of active dialogs, and, as result - on number of active calls. And this RFC looks like supported on Cisco gateways: U X.X.X.X:59104 -> X.X.X.X:5060 INVITE sip:aaaaaaa@X.X.X.X:5060 SIP/2.0. Supported: 100rel,timer,replaces. ^^^^^ Min-SE: 1800. ^^^^^^^^^^^^^^ User-Agent: Cisco-SIPGateway/IOS-12.x. Question: is this RFC/functionality planned to be supported in SER ? If not - are there any good intro on "How to write SER module by yourself" ? :)