Apple may have blocked the Google Voice internet telephony app from its App Store, but Google has executed a nifty end-run around the blockade by releasing Google Voice as a web page that is accessible by any HTML5 web browser. Simply direct your iPhone or Palm Pre to google.com/voice to make calls from your Google Voice account (Android and Blackberry owners can just keep using their native Google Voice apps).

Our Top 7 Disruptions of 2009 included both the Google Stack and HTML5 mobile apps, putting this development squarely in the cross hairs of two important trends. In Apple’s ultimate nightmare scenario, its rejection of Google Voice could come back to haunt it, should history look back on this moment as when the scale tipped away from Apple’s App Store model and towards HTML5 apps that duplicate the functionality of downloadable apps without requiring custom development for each smartphone platform.

Indeed, the ability to add a web page to one of the iPhone’s home screens — proprietary Google Voice icon and all — creates a user experience that is nearly identical to using apps which run off the OS rather than the cloud, and presents differences that almost nobody who uses it will really care about.

It took the desktop computer decades to move from the installed software model to cloud-based software as a service, and it may never get there completely. (Aviary is great, for instance, but it can’t duplicate the functionality of Photoshop, Pro Tools and Final Cut Pro.) On the mobile side, the downloadable software model invented only one and a half years ago by Apple may already have met its match in HTML5, judging from the smoothness of this app.

The mobile web version of Google Voice switches to the iPhone’s normal calling function in order to place calls, similarly to the way the web-based version of Google Voice can connect your home, mobile or VOIP phone to other people’s phones for a call over whatever network that device uses (updated). The system routes the call through AT&T’s cellular voice network by connecting your call to local Google Voice number, potentially saving you money on international calls.

The process works seamlessly, and the app feels about as fast as the Google Voice app that was blocked by Apple probably was. (A Google spokeswoman told Reuters that the company has not heard anything new from Apple about the approval of the native Google Voice app for the iPhone.) Plus, you get access to lots of advanced Google Voice features from within the phone: voicemail transcription, forwarding of SMS to an e-mail account or Skype, screening, integration with your web-based Google Voice account, and of course the ability to answer all of your phone numbers from a single handset.

Dialing a number using this mobile app requires one extra step in Google Voice as opposed to using the iPhone’s own number pad, as noted by Gizmodo. But a bigger issue for those who have yet to make a concerted leap to Google Voice is that the app cannot access your iPhone’s contact list.

Exporting your iPhone contacts and importing them into Google Voice is a hassle, but there’s an app for that (Export Contacts; iTunes link; to avoid contact information ending up in the wrong field, set the separator as a comma and double quotes as the delimiter). Other software is available for porting contacts from iTunes to a CSV file, which is what you need to import your iPhone contacts into your Google contacts list, or Google Sync can merge the Google and iPhone contacts lists via Exchange and keep them (updated) — just back up your iPhone contacts first. On the upside, if you already use Gmail and have plenty of friends who also do, many of their numbers show up in the Google Voice contacts list automatically.

Tapping the plus sign in the iPhone’s browser lets you add a Google Voice bookmark to the iPhone’s home screen, so that launching it feels just like launching a native app. And the use of the browser offers one minor advantage over a standard app: standard forward-and-back navigation using browser buttons.

Google Voice has a notorious relationship with Apple, although other areas of Google (Gmail, Search and YouTube) are installed on every iPhone by default. Apple rejected the Google Voice app, which led to an FCC investigation. Apple claimed that its policy requires blocking any app that duplicates core phone functionality.

If anything, the problem with this HTML5 version of the app is that it doesn’t duplicate enough core phone functionality. Without the ability to make internet phone calls over Wi-Fi (i.e., without using your over-the-air minutes), Google Voice is more of an add-on to existing functionality, which begs the question: Why did Apple block the Google Voice app in the first place? Are a contact list, voicemail system and short text messaging really “core” functions? Is voice just another feature in a phone? It’s looking that way.