A neat IMS feature: CNAM in SIP headers allows you to set a display name to be shown (as well as the calling number) on incoming VoLTE calls just by adding a username to the from header
SIP has got a multitude of ways of showing Caller ID, PAI, R-PAI, From, even Contact, but the other day I got a tip (Thanks John!) that you can set a name as the Caller ID in the “Username field “display name” part of the P-Asserted-Identity for the leg from the TAS to the UE, and it’ll show up on the phone, and they’re right.
Read more: 
LinkedIn:
Hi nick.P-asserted ID,Which is a privacy header.And It has a fix standard defined by both the regulator as well as 3GPP so I dont think this will be allowed by any IIMS network in the world.There are few reasons for it first thing is when you have P-asserted ID,From number and contact header all three usually from number and PAID carries the MSISDN,that is called IMPU(Public Used ID).When both are present in invite Node will give priority to PID to be printed in the Diameter CCR and ACR used in both online offline charging.you mention about contact header contact header usually carries either imsi IMEI or Both wich either one of them named IMPI(Private user)which is alsi printed in the CDR for athenticity purposes.No telecommunication operator will allow any thing elase to come through those parameter other than the once which I have mentioned since those parameters will do a huge roll ina call flow.One more thing I wanted touch is that you said something about a call leg between mtas and UE .MTAS never sends a call directly to user never ever which is a not correct as well.to elaborate it more in any M to M call flow there should be at least 2 MTAS es those one for the originating part and the other for the terminating party even though it shows you as one node MTAS is not one node it is two nodes those are MMTEL abd SCCAS which handle th MObility management and call control. Thanks
