If you’ve already been introduced to the wonders of Google Voice, then you probably know about most of its handy features: the capability to direct calls to multiple phone numbers, voicemails delivered straight to your email inbox, and free texting. But on your Mac, its features don’t have to be confined to your Web browser, thanks to Eric Horacek’s $5 GrowlVoice (Mac App Store link).

As its name suggests, GrowlVoice marries the power of Google Voice with the low profile of the Growl notification system. When you receive a text, miss a call, or get a voicemail through Google Voice, you get, on your Mac, an unobtrusive pop-up notification alerting you to this fact. GrowlVoice’s menu-bar icon also turns blue and displays an updated count of the events that you’ve missed.

But GrowlVoice takes things even further by letting you actually use many of Google Voice’s features. Click on the notification for a text message, for example, and a box drops down, letting you view your conversation and even reply to the text. Click on the notification for a voicemail, and you can read the message transcript and even play back the actual message right from the menu bar. Click on the notification for a missed call, and you’re prompted to return the call.

As with most programs that use Growl, GrowlVoice’s notification styles are tweakable via Growl’s own preferences—you can change the notification theme, colors, opacity, and duration. (Note that if you don’t have Growl or don’t want to use it, GrowlVoice also offers its own built-in notification system, though its options are less customizable.) A Suppress Notifications option lets you temporarily silence these pop-ups if you need some quiet time.

Delving into GrowlVoice’s menus lets you mark messages as unread, archive them, or delete them, as well as view information such as timestamps, though the menus can occasionally get somewhat unwieldy. The program also integrates with either Google Contacts or Mac OS X’s Address Book in order to assign friendly names and pictures to otherwise anonymous numbers.

For the most part, GrowlVoice works swimmingly, staying out of the way when it isn’t needed and popping up only when you’ve asked to be alerted of something. You can place calls with any number associated with your Google Voice account right from the menu bar icon. In addition, if you have Google Voice configured to use Gmail’s Google Talk feature, you can open a Web browser to your Gmail inbox and use GrowlVoice to kick off VoIP calls. (Unfortunately, Google doesn’t currently allow outside clients to make VoIP calls without using a Web browser.)

My only real complaint about GrowlVoice—aside from the aforementioned Google-enforced VoIP shortcomings—is that its interface is badly in need of some fit and finish: Parts of the app feel decidedly un-Mac-like. However, the developer has demonstrated a commitment to frequent updates and tweaking. Plus, when the functionality works so well, I’m willing to forgive some rough aesthetic edges.