While Speech Server is apart of Office Communications Server, the two do not rely on each and actually do not integrate with each other out of the box. However that doesn't mean it can not be done.
There are two main scenarios which I am always asked about are:
1.) Communicator Calls to Speech Server
2.) Transferring Speech Server calls to Communicator
Calling Speech Server from Communicator
The first thing you need to do is setup a static route in OCS to Speech Server. Here you will need to assign a sub domain, something like ivr.domain.com. This tells OCS to route all calls where the domain contains ivr.domain.com to Speech Server.
Next in the Speech Server administrator console you will need to add the OCS Front End Server as a Trusted SIP Peer on non default ports, such as 5068 for TCP and 5069 for TLS. This is required as OCS doesn't handle the 302 Redirect Messages that Speech Server uses, by assigning non default ports we "turn off" these SIP messages. You will also need to enable Mutual TLS. More