VoicePod has connections for an external mic and speaker, so you can hide it in a rack somewhere and trigger via wakeup phrase ("Hello VoicePod") or a button on the touchpanel.
I have tested VoicePod for a conference-room scenario, and it works well for what it does.? The lack of free-form dialing killed it for that project (can't recognize a string of digits without prompting for each one).
The library of recognized commands can only be expanded without cooperation from VoicePod, which they offer as a paid service.? The library of speech files is the same way.
Keep in mind that it's not free-form text recognition like people are used to with Siri, it's strictly menu-based.? If your application fits well into the existing menus (designed for residential A/V control), you're golden.? If not, you need to pay for custom programming.
The 232 interface is sensible and easy to handle from Crestron.
I don't know of any alternatives that work without Internet connections.
The problem is that client don't want to get it through any other device or app. bcoz they will not allow anyone to any new device which is physically viewable and is not included in their interior design. They want the integration in the same app and specially push to talk will not be accepted by the client.