Check out the eWeek article about GoogleVoice and Gizmo. Seems the Nexus One isn't the only thing that Google is now "leaking" over.
Here's what I think.
1) Gizmo5's assets brings GoogleVoice the missing soft client on multiple platforms except the iPhone. That will have to wait. Macs, PCs, Symbian and Android will be their markets first. Symbian on the Nokia smartphones. Gizmo previously had a Truphone like app on them.
2) Gizmo's softclient becomes a lot more. Expect the Flash based Gizmo client to become embedded in Chrome and that making calls from Chrome becomes very easy.
3) On Chrome OS Netbooks, watch as Google expands the calling to integrate video. Already Google has video with Google Talk, but so does Gizmo so making it part of the operating system or browser adds a whole new dimension. SightSpeed has browser based video calling, but only inside Internet Explorer.
4) I would expect that tagging of Google Voice messages and being able to associate them to projects inside Google Apps becomes part of their roadmap.
5) Google Voice's international calling capabilities get expanded. You'll be able to add international phone numbers to be your termination numbers. You will also likely be provided the opportunity to purchase Google Voice In numbers.
6) As LTE and WiMax take hold the phone number on the device becomes less relevant. Because Google Voice and Gizmo are SIP based your email address can be called.
These and a lot more new features will play major roles with Google Voice/Gizmo simply because what's possible is what Google sets out to do. What's also clear is they don't really care about the carriers. To them the mobile operators are dumb pipes whom the customer pays for access. Everything else will be from Google.