If you're one of the lucky ones to have scored an invite to Google Voice, check out VoiceCentral. It's a very slick application which integrates well with the iPhone, making it possible to make calls through your Google Voice (or GrandCentral) account.

Why would you want this? My primary reason for wanting an application for GV is so that I can make calls and have my Google Voice number appear on the Caller-ID.

VoiceCentral makes this a simple process. When you first install the app, it asks you to select your iPhone number on the Settings page. When you make a call through the app, it happens in two steps: 1) your iPhone rings (this is Google Voice's servers calling your iPhone), 2) your call is connected.

Why is this important? If you end up leaving a message for whoever you are calling, their voicemail system may give them the option to call you back at the number you called from. Our landline phones also make it easy to return calls from the caller-ID list. As a Google Voice user, I want those calls to go to my Google Voice number, not my iPhone.

If you're a fan of Google Voice, you know that having a central place for all of your voicemails is great. Google Voice will transcribe those voicemails (my favorite feature, although sometimes having a computer try to decipher my friend's "late weekend night" messages does lead to some interesting "translation issues").

VoiceCentral will let you access not only those voicemails (in a style very similar to iPhone's own Visual Voicemail) but if you tap on the arrow, it will also show you the transcription. You can even read the message without listening to it, which is especially handy for checking messages when you are in a meeting, a movie theater (oh, like you've never!), or anywhere loud enough that you might not be able to hear it. The transcripts can also be copied (on iPhones running OS 3.0 or later, of course) and pasted into notes or emails if needed.

As you'd expect, VoiceCentral also integrates with your existing iPhone contact list, and there's also a keypad which allows you to make calls or send SMS.

The "Send SMS" feature has had some issues, but Riverturn has a newer version which fixes the problem. As you are no doubt used to hearing by now, they are waiting on Apple to approve the newer version. It's also important to note that there is no way to designate any application except the built-in Phone app as the default, so any phone numbers which you tap from email messages or web pages will open in the built-in app, rather than in Skype or other telephony apps.

Google appears to be readying its own GV iPhone app for release, although it hasn't made it into the App Store yet. Anyone familiar with the approval process knows that could mean it is hours, days, or weeks away from being released. The Blackberry and Android apps are already available.

Is $2.99 [iTunes Link] too much to spend on an app when there may be a free alternative right around the corner? Not for me. In fact, the only thing which keeps this app from replacing the native Phone app on my dock is the lack of a "Favorites" tab, which I use for nearly all of the outgoing calls I make on my iPhone.

In the world of Mac telephony software, there's one leading product -- Parliant PhoneValet. Parliant today released version 6.0 of PhoneValet with some new features that make it even more attractive to small business owners. Those features include:

• Live receptionist -- Want to have a real person answer and direct calls? PhoneValet now allows a receptionist to perform those functions.
• Call out to deliver voice mail -- To keep employees in the loop when they're on the road, PhoneValet will call their cell phones to deliver important voice messages.
• Change greetings remotely -- Prior to version 6.0, PhoneValet users had to be sitting at a computer to record new outgoing voice mail greetings. Now they can do this from any phone.
• Mailbox privacy -- Messages for others on a shared PhoneValet server are now hidden.
• Network dialing -- Desktop dialing is now available to any PhoneValet or PhoneValet Anywhere user on the network.
• Shared phonebook / call log editing -- PhoneValet Anywhere users can now edit phonebook entries or trim call logs.

PhoneValet 6.0 is available for US$169.95, which includes a USB phone adapter, or to existing owners of PhoneValet for US$39.95. PhoneValet Anywhere, which allows users to access their PhoneValet messages from Windows PCs and iPhones among other features, is an available add-on for US$59.95.

Internet Telephony Provider rf.com is getting ready to launch its iPhone-specific PBX service. The service allows you to place calls both internationally and to online providers like Skype using your normal iPhone minutes. So if you have a friend who's on Skype but has no Skype In access, you can call them just as if they had their own number.

RF operates its own PBX, which you connect to over a web client. Once there, it finishes routing the call using VoIP and connects it to your iPhone handset. You use your iPhone calling plan minutes whether you're talking to a guy down the block or your buddy in Beijing.

Because their client is web-based, it works with 1.1.4 and earlier iPhones as well as 2.0 iPhones and later. All the heavy lifting happens at the RF servers, connecting you through the VoIP networks. RF's service is free and still extremely beta -- so be prepared for growing pains as they stabilize their software and roll it out. RF Founder/President Marcelo Rodriguez says they're planning on keeping the basic service free for the forseeable future. They are monetizing by reselling the service to VoIP service providers such as PhoneGnome and will be offering premium features at a later date.

I recently stumbled across this article about Jajah and the iPhone. Jajah, for those of you unfamiliar with the service, is a free telephony provider that lets you make local and international calls[1]. You place the calls at the Jajah website, and they connect first to your regular phone and then to the phone you're calling and they connect the two together.

So why would Jajah be of interest to the iPhone, which presumably has its own calling plan through AT&T/Cingular? Well for one thing Jajah allows you to place international calls using local incoming minutes. Jajah calls your phone before connecting you to your party. Second, if you subscribe to Cingular's "Metro Plan", which offers free incoming calls, you wouldn't use any minutes at all. Of course, this applies only to users in the free calling regions listed on the Jajah website.

It's a nifty article. I recommend you read it all.

[1] Jajah is also the website of choice for April Fools jokes. I'll let you google the details.