[Freeswitch-users] How to modify P-asserted-id on UPDATE?

Hi, I use to set send-display-update in order to show external caller number on phones, even after an attended transfer or a call pickup. This number is saved on phone's call history and can not be used to call it again because we use zero as prefix to call outside. That's why I'd like to add a zero to caller number used un UPDATE P-asserted-id value. How can I do it? For example: - A (mobile fone 312345) calls B (extension 201) - C (extension 203) picks up that call - C talks with A and on C display I see 312345 due to sip UPDATE P-asserted-id I'd like to send 0312345 on that P-asserted. Is it possible? Thank you. chrisbware