''In its most straightforward, mobile VoIP is voice over IP over cellular and Wi-Fi networks, but that's still three to four years away. When people talk about mobile VoIP today, they're referring to voice over wireless LANs,'' says Svetlana Issaeva, manager of Communications, Media and Technology Research at Pyramid Research in London.
There are currently three variations of mobile voice over IP being researched or already in production in consumer and enterprise markets:
''Mobile voice over IP to me today is going to our New York office and logging into my IP phone there and it appears as if I'm in my Minneapolis office. This is base-level mobility,'' says Chris Ferski, director of Information Technology at Goldsmith Agio Helms, an investment banking firm in Minneapolis.
''True seamless mobility will let me go anywhere and do what I need to do and not have to worry about phone numbers and contact information -- it will all be invisible and transferable,'' he says.
Ferski himself says he has different levels of mobile voice over IP that he's working through. The first is simply being able to have the company's 110 employees easily move between the five corporate offices in Chicago, London, Los Angeles, Minneapolis and New York without having to deal with moves, adds and changes. He gets this functionality from his Nortel Networks VoIP network.
He also uses Nortel's softphone tools to let his users access the VoIP network from the road using their laptops and headsets.
Next year, he plans to add to this mobility by installing wireless LAN-enabled mobile handsets for use in the company's public spaces. Ferski says high-end bankers could then log into those handsets, which would be wirelessly connected to access points, and carry them into the boardrooms and other meeting areas and not miss important calls about deals that otherwise might go to their desk phones.
While Ferski is working within the confines of the wireless LAN network to gain voice over IP functionality, TalkPlus, Inc. is encouraging users to make more of their cell phones for mobile VoIP capabilities.
''Mobile VoIP to me is having a device that lets you drive down the highway at 60 miles an hour and get all the features that you'd have on a voice over IP connection,'' says Jeff Black, CEO of TalkPlus in Menlo Park, Calif.
The features TalkPlus enable include multiple numbers or identities to one phone, voice mail for each of those identities, group conference calling, and low-call rates. ''You can have one number or 10 numbers and each of them have individual controls,'' he says.
''You're in the cellular world all the time. You want to extract the cost-savings of the voice over IP in the broadband world into cellular service,'' he says. Black claims his service offers rates as low as two cents a minute for calls in the U.S., and three and a half cents a minute overseas to cities like London.
He adds that the company is able to achieve this by running voice on the voice channel and data and other information over the signaling channel on carrier networks. TalkPlus co-locates its equipment in neutral facilities, like Equinix, so it can plug directly into carrier switches.
TalkPlus is currently a beta-version hosted service, where consumers can go to the company's Web site, www.talkplus.com, create an account with multiple identities and have the application sent to their phone via an SMS message. Black says more features, such as links to LDAP directories and an enterprise version, will be added early next year.
Though these innovations are impressive, Randy Giusto, group vice president of Mobility, Computing and Consumer Markets for International Data Corp. in Framingham, Mass., says the real holy grail for mobile VoIP is the convergence of voice over Wi-Fi and cellular networks. He says that's where companies will truly see a cost-savings.
''There are a growing number of employees making cell phone calls on campus,'' Giusto says. If they could access a wireless IP network from their handsets, the savings could be in the range of 25 percent to 28 percent.
''The grand vision is that you're on a call and in the building you're on the Wi-Fi network, and then you walk out to the parking lot and you automatically switch over to the cellular network. But there isn't a clear software-based handoff that's transparent to the user yet,'' he says.
But there has been a ''chicken and egg'' mentality about creating new handsets, services and infrastructure. ''IT organizations are saying if I can save that much for voice calls, I'd be willing to do it. But the handset companies are waiting for orders and interest,'' Giusto says.
This is a problem that Sanjay Jhawar, vice president of Marketing and Development at BridgePort Networks, Inc., is trying to solve. Jhawar is chairman of the steering committee for MobileIgnite, an organization formed in January to create open solutions for the merging of mobile voice over IP on Wi-Fi and cellular networks.
''Our goal is for users to be able to have a single phone that would be a mobile phone when you were in the wide area network outside the home and office environment and also a voice over IP phone with Internet calling when you're near a Wi-Fi network. And you'd have the same number across both networks,'' he says.
For this to happen, Jhawar says there has to be a convergence at the device and service layers. ''There are elements that have to be looked at in the mobile network, fixed networks, media gateways, and softswitches,'' he says.
Though it seems too complex for there to be progress, more than 20 companies, including VeriSign, Inc., Net2Phone, Inc., Kyocera Wireless Corp., and Boingo Wireless, Inc., have joined the organization.
Jhawar says their charter is threefold: to create interoperability between handsets with Wi-Fi and cellular; to create IP Centrex to mobile network interoperability; and to create interoperability between SIP and mobile environments.
For Ferski, this sounds like a dream come true.
''I'm looking forward to devices coming out to support this. The more options we have to connect seamlessly and to seamlessly hop onto various networks, the better,'' he says.