Google keeps "encouraging" me to install the Google Hangouts software to replace Google Talk. I've avoided this to ensure I don't screw up my SIP connectivity. But it would be very helpful to have a blog or forum post that advises users of your service on this. I couldn't find such info using your forum and blog search tools.
I don't believe that using Hangouts will have an adverse affect. If anyone else here has used it, please chime in. I'll test it out myself.
I've seen several comments on the internets that suggest an emerging issue here. For example:
I currently use GVGW for inbound calls, but place my outbound calls via my web browser, ringing to the Google Talk/SIP Gateway. So I am wondering if that configuration will still be supported.