If you want to end up with a conference, no, still not a feature.
If you want to reach out to many users at a time, and have one answer the call, then use a line group with any algorithm.
Informacast is for paging, so yeah, if you want paging, you can use it.
It has nothing to do with callmanager's version. Call Manager just forwards the group call number to the voice gateway.
TCL script running on a callmanager express, which creates conference room and makes predefined called numbers join the conference room solves the problem.
I have implemented and it is working. You need IOS gateway.