While everything at VON is, of course, billed as breakthrough, disruptive, playing field-changing technology, one of the most potentially disruptive new developments made its debut before the show, on Monday at San Jose-based HelloSoft’s open house.

When Alexander Graham Bell uttered those fateful words, “Mr. Watson, come here I want you” I’m sure that no one was reporting about the voice quality.

So when I experienced a seamless WiFi-cellular call handoff yesterday, I wasn’t focused on the details so much as the fact that this was actually working. With people calling seamless handoff the “holy grail” of convergence, well, I was excited to see it work.

I’m pleased to report that unlike much new technology, it didn’t just work the first time. It pretty much…worked.

While the handoff was audible, sound quality was acceptable. The phone has a single phone number — HelloSoft’s other dual mode phones have separate numbers for the WiFi and cellular networks. The handset shows network strength for both networks as well as highlighting what network is currently carrying the call.

While seamless handoff isn’t going to change the world as profoundly as Bell’s invention, it has the potential to change mobile telephony pretty significantly.

Of course, some question if voice WiFi — even in its dual-mode incarnation — the tree to be barking up? Especially as at least one carrier recently dropped its dual mode phone.

There’s plenty of opportunity, says Ron Victor, HelloSoft GM, Marketing and Business Development, although he does say that the technology-focused business model for WiFi phones has been flawed from the get-go.

“People don’t care what infrastructure you’re on,” he explains. “They want good voice quality at a very low price. When was the last time you said, ‘Is my call going through an HSDPA network?’ The assumption that people are going to jump to WiFi was fundamentally wrong. What’s the value proposition?”

The Skype-only handset illustrates a business model that does make sense, Victor says. “Why do people use Skype? Because it’s free. The Skype handset is more convenient, more flexible, more grandma-centric. You have a value proposition.”

“In voice over WiFi, the only way you’re going to entice me to use it, is that you’re going to slash my phone bill,” he continues. “But if you drop it to $25 a month, well Vonage has done that already. But if you tell me you’re going to drop my phone bill to $5 a month, then you’ve got my interest.”

One of the value propositions Victor sees for a dual mode phone is the potential to save businesses sacks of money on corporate cell phone bills. “Companies are already paying for cell phones for their employees,” he explains. “There are huge savings if you can move mobile phone calls to the enterprise network. Industrial applications — that’s where voice over WiFi is going to happen.”

Or as someone else I encountered at VON, Jeff White of Cognio put it, “The killer app for wireless is VoIP. The killer app for VoIP is wireless.”

HelloSoft is showing its line of dual mode phones at VON. The company is also running shuttle buses to its open house down the road where visitors can try out the seamless handoff for themselves.

HP today announced its new smartphone, the HP iPAQ 500 Series Voice Messenger, that brings some real smarts to the world of smartphones.

The GSM/WiFi voice and data device is designed for business users rather than teenagers. It runs Microsoft Windows Mobile 6 and is geared for hands-free operation with a speech interface called “Voice Commander.” This lets the iPAQ replace the QWERTY keyboard with a familiar telephone keypad.

One of its most unique features is a voice-reply-to-email feature that eliminates the typing from answering email, something long overdue in the PDA world. This will clearly make mobile email more popular.

The iPAQ also integrates with any SIP-Based IP-PBX to eliminate the need for wired phones at those desks we never spend much time at anymore.

For IT managers, the gizmo provides over-the-air device-management capabilities for remotely managing security settings and applications, data, and corporate networks. This is a useful feature for dealing with lost or stolen phones.

The HP iPAQ will be available in the Spring of this year through HP directly and some dealers. A data sheet is available but HP hasn’t released any pricing. Some are saying the device will be in the $300-$400 range.

You’re away from the office and discover you need an email address that’s in your desktop address book. But you can’t get it with the one device you do have with you — your cell phone.

Remoba of Santa Clara, CA thinks you should have another choice besides a PDA and a costly wireless data plan. The three-year-old company’s mission is to bring your desktop to your plain-jane ordinary, un-smart mobile phone.

Remoba offers a suite of applications that connect desktop applications like address books and calendars to cell phones without a mobile carrier’s data plan. Instead, the company’s service connects to your desktop using the air minutes you already pay for — the same way, for example, that you download your Ride of the Valkyrie ring tone.

In effect you get Blackberry capabilities with any CDMA or GSM phone. Remoba applications are offered through several mobile carriers in the U.S., South America and India. All are priced under US$10 per month.

One of the company’s offerings, RemoMail, is particularly handy. It lets you check and send your email from whatever cell phone and service plan you have today. It’s a quick fix for travelers who don’t need or want to deal with a Blackberry or other mobile email device and is priced proportionately at $1.99 a month.

RemoMail delivers email headers to your phone in batches of five at a time. You can decide if you need to read the entire message, delete it, or reply to it. You can connect to as many as seven different POP or IMAP email accounts.

RemoMail is most easily available right now through Verizon’s Get It Now program. You can also use the application with other carriers, although the configuration is a little more complicated. (Robinson promises to set me up with a Sprint version I can use on my Palm Treo, report to follow.)

This month Remoba launched its newest application, iPhonebook, which lets employees access corporate directories from their mobile phones. Especially useful for mobile workers, like sales reps, real estate agents, and general contractors, the service synchronizes information in both directions — from the desktop to the phone, and phone to the desktop.

For example, one iPhonebook client is a northern California construction company. iPhonebook gives the company’s crews all the contact information they need for customers, subcontractors and corporate contacts for each job.

“We deliver a company’s address book to anybody who’s mobile and needs their contacts to stay fresh,” says Remoba VP of Sales David Robinson.

“Most business people who are traveling don’t have all those different services available, for example, when they’re stuck in a plane for two hours, sitting on the tarmac,” explains Robinson. “But even if they have a candy bar phone with a mini keyboard, we make it into a tool they can use ‘right now’ to keep things moving.”

“We believe that the momentum is in this part of the market,” says Robinson. “Smart phones are only one percent of the market. But everybody needs better connectivity than they have now.”

Truphone company founder Ed Guy is one of his company’s best customers. “I’m a multiple device person. My cell phone doesn’t work in my house. So when I’d only need one device I’d have to carry two.”

Now he only carries one, thanks to UK-based Truphone’s long-awaited “mobile VoIP” for the Nokia N80, which was launched today. Currently the service is only available for Cingular and T-Mobile customers because Nokia doesn’t deliver WiFi-enabled phones for the other services.

Truphone’s “secret sauce” is simplicity.

You download the software by sending an SMS with the letters ‘TRU’ to a specified number. The phone is provisioned automatically and uses your existing address book.

There’s no sign-up charge or monthly fees. You only pay for calls outside the Truphone network. All you have to do is start making calls — no special numbers or key sequences. “It’s the type of thing your grandmother could use,” explains Guy.

When you dial a call Truphone first tries to route the call over the Internet. If that doesn’t work, the call is sent over the GSM cell phone network. There is reconfiguration that has to be done when you move between WiFi hotspots. But this job is still a one-key operation.

The obvious application for Truphone is cutting airtime charges, which add up very quickly for overseas calls. For example, GSM calls from the US to the UK are $0.34 per minute while the same call placed over the Truphone IP network is $0.024 a minute — less than a tenth the cost.

And there are other handy applications as well.

If you live in a place with poor cell coverage (like Ed Guy’s house in rural New Jersey) you don’t need another handset to make calls using your WiFi network. Another use is during a power outage. If you can find an operational hotspot, you can still make calls.

Now, some are saying that Truphone offers “seamless handoff” between cell and WiFi networks. That’s not quite true.

Yes, you don’t have to do anything but dial calls. But once the call is placed over one network it’s not going to move between the cell network and the WiFi network the way calls move from one area of cell coverage to another.

“We do have the technology for roaming between GSM and WiFi,” explains Guy, “but it hasn’t been deployed.” High battery power consumption is the issue, Guy says, and the company is working on a hand-off method that won’t interfere with battery life.

Truphone hopes to bring its dual-mode calling to more phones in the coming year, although Guy won’t commit to any dates. “We’re seeing a lot of user demand for VoIP-enabled phones,” says Guy. “It should promote the proliferation of hotspots.”