Google Voice is a great solution for many people. You have just a single number that can be handled by many devices, you can even change your line without having to give everyone you know the new number, you Google Voice number is always the same and you can get transcripts of your voice mails in Gmail, pretty convenient if you ask me.
There is, however, a big issue with Google Voice, and that is that Google doesn't seem to be paying too much attention to it yet. The Google Voice app for Android is pretty bad, and you can't use Voice with any other app, nor Hangouts nor any third-party app.
Koushik Dutta set himself to fix this for the millions of CyanogenMod users and announced Google Voice SMS integration into CM10.1, not only in the stock messaging app, but any third-party app you might like to use. We know that Google is planning to throw Google Voice into Hangouts but since that hasn't happened yet and we don't know when it will, this is the best solution so far, too bad it's limited to CyanogenMod.
This is great news for any CM users who hate the Google Voice app, but also, it could turn any other Google Voice user into Cyanogen just for this feature alone, but we also know that CyanogenMod has a ton of amazing additions like the recently added camera to the quick toggles, night mode and shortcuts in the lockscreen.
This comes straight from Koush's Google+ page:
0) Google Voice must be installed with notifications enabled (for now).
1) Install a recent +CyanogenMod nightly. July 1st or later. You need the SMS middleware patches I put in for PushSMS. (see Gerrit)
2) Push this apk to /system/app: http://download.clockworkmod.com/test/babel-signed.apk adb install will not work. The app requires system/signature permissions.
4) Start Babel, choose your Google Voice account. Authorize it.
6) Click the "Accessibility service" button, and it will direct you to settings. Enable "Babel".
No, Babel is not the final name.
How it works:
The app will sync your existing Google Voice messages into your messaging store. New Google SMS will be received as if it were a normal SMS.
When you send a message out from your messaging app, it goes out via Google Voice.
Other than the fact that he skipped steps 3 and 5, the process is pretty simple, but it comes with a warning: "This comes with no support, and is nowhere near complete." Keep that in mind if you want to give Babel a try.
He's just starting and we all know Koush is a great developer and the final product will be perfect for every Google Voice user. Give it a try now or wait for the app to be a bit more advanced, it's your choice. I personally can recommend it, I haven't tried this particular app, but if it's already being offered for people to try it, then I'm sure is pretty usable. And it can't be worst than the stock Google Voice app...