Hi Sanjeev Sharma,
While providing Announcement , GMSC Wont connect to IVR it will connect to (G)MSC Announcement System.This is as per the outcome of the MT Call Process Result.
For announcement it wont send any IAM.or any other Message.Since the incoming call already SEIZED a device with IAM it will play the announcement on that Device.
If you do Tracing with Analyzer and TAP that Circuit you can realise this.