[SR-Users] Billing party and radius accounting

Hi folks, I have a problem with setting billing party in my radius messages. My accounting is done by CDRTool via radius messages to radius server. The thing I don`t know is how to set billing party variable (by default $avp(s:billing_party) with reliable value. I can try adding Diversion header and fill the variable with it, but can I trust the Diversion header? When UAC sets redirect(302) and Invite comes, he replies 302 and Kamailio passes this message to origin. However is it possible to change Diversion header by UAC? This could be way how to make free calls and bill it to someone else. I was thinking of uac_redirect module. If I get it right this module saves original number in memory and does not use message itself to store it. In documentation there is written that accounting can by done by setting modparam("uac_redirect", "acc_function", "acc_rad_request"). Even when I use exported function set_accept_filter() the accounting itself isn't done. I`d like to get original number from module uac_redirect and set it to $avp(s:billing_party). This would solve the problem of billing forwarded calls. Am I getting it right? Is there anything else what can be passed to billing party variable to make correct bililng? I'm using kamailio 3.1.x and CDRTool v 8.0.6 Thanks, Efelin