Google Voice is a great service, but because of the iPhone's restrictions the official app doesn't offer an ideal experience. If you'd like to improve the way Google Voice works within iOS, here's how you can do it.
While there are definitely fewer options when you haven't jailbroken your iDevice, there's still plenty you can do with Google Voice. In some cases, the non-jailbreak options may even be preferable. We're going to take a look at both so nobody's left out.
Calling
The official Google Voice app was a welcome addition to the iPhone when Apple finally allowed it into the iTunes App Store. That said, it's not perfect. It offers a decent experience, but GV Mobile + ($3, iTunes App Store) offers a better one. It provides more calling options, better voicemail viewing and playback, plus great call forwarding management. If you're not satisfied with the Google Voice app you get for free, GV Mobile + will provide a nice upgrade.
If you've jailbroken your phone and want to fully integrated Google Voice calling into the default iPhone dialer, you'll want to check out Phone GV Extension ($3, Cydia) or GVIntegrated ($2, Cydia). The Phone GV Extension has been updated for iOS 5 but GVIntegrated has not. Both provide the same function. When you make a call, you'll be presented with the option of calling from your iPhone's number or your Google Voice number. That's all there is to it, but it makes outgoing calls via Google Voice significantly easier.
Text Messaging
One of the biggest annoyances of the Google Voice app is that when you receive a text message via push notification, the app hasn't actually updated with that message. Furthermore, updating generally requires a manual swipe to remind the app to actually check. This is annoying. Fortunately, you have two really great alternatives.
As mentioned in the calling section, GV Mobile + ($3, iTunes App Store) is a great alternative to the official app and that goes for your texting needs as well. Push notifications and updates tend to work a bit better, and the interface is nicer over all. If you'd prefer to have your Google Voice texts separated from calling, however, Infinite SMS (Free, iTunes App Store) is my favorite option. It is essentially a replica of the built-in Messages app for iPhone, but works with your Google Voice account. The only downside is that it's ad-supported, and if you want to remove ads you have to buy the paid version for $5. That seems a bit high when you can get GV Mobile +, which does a lot more, for $3.
If you've jailbroken, you also have the opportunity to use the SMS GV Extension ($3, Cydia) to fully integrate Google Voice into the official Messages app. The downside is that you lose the ability to use iMessages, but you also gain the ability to use popular messaging app biteSMS with Google Voice. Because biteSMS can replace the official Messages app and send from your phone, if the SMS GV Extension overrides the number that app sends from it'll work with biteSMS.
UPDATE: Apparently the SMS GV Extension does work with iMessages. (At least that's what we're hearing.)
Got any other great ways to better integrate Google Voice with your iPhone? Let us know in the comments!