The "Informer," writing in A Week in Wireless #268 today, quotes Li Mo, Chief Architect Officer of ZTE USA, apparently speaking at this week's IMS World Forum in Monaco, as saying "We analyzed hundreds of contracts, and practically all of them are softswitching, hardly IMS at all."
I wasn't there to hear it, but this strikes a chord. I have now seen the internals of operators' networks built by Ericsson, Nokia and Huawei and referred to as "IMS networks." In each case, what they have is voice services controlled by a pre-IMS softswitch (based on 3GPP Release 4) plus some kind of SIP infrastructure that they are using for new applications like Push-to-Talk.
I have even seen a confidential sales presentation from a major equipment provider using the term "IMS R4." Since IMS was first defined in the 3GPP release 5 specifications, "IMS R4" is not IMS. In credit to the company involved, this was obviously the act of their field sales guy, as Googling "IMS R4" returns no public mentions from that company.
In any event, what appears to be deployed today is pre-IMS or, as Dr. Li Mo says, "hardly IMS at all."