Nokia is one of the biggest makers of cellphones that include chips for using Wi-Fi, the short-range wireless technology. Some high-profile devices are equipped with the technology, including Apple's iPhone and some BlackBerry models from Research In Motion. The soon-to-be-released G1 Google phone from HTC and T-Mobile also sports a Wi-Fi chip.
For Mark Laris, a Dallas-based nuclear engineer who travels the world running his consulting business, the technology saves him thousands of dollars a year on international phone bills.
Wi-Fi chips and Voice over Internet Protocol, or VoIP, let him do most of his business and personal calls over cut-rate phone services that work over the Web. His only cellphone bill is a 1,400-minute-per-month family plan from AT&T that he shares with a business partner.
"I always make VoIP calls," he said, adding that the call quality was as good as with a traditional mobile phone service.
He has access to the VoIP services by using a Nokia phone that has a Wi-Fi chip similar to the ones that allow laptops to connect to the Web in smaller venues like coffee shops.
The new phones are capable of operating exclusively with Wi-Fi - they do not need to use a cellphone network at all - and when the user is not in a Wi-Fi "hot spot," calls are routed to the Wi-Fi carrier's voice mail service.
Still, mobile VoIP is a fledgling field.
In the United States, T-Mobile sells Wi-Fi phones and Internet calling plans that cost $10 a month, on top of regular fees. It is the only U.S. carrier with such a package. The market is also filled with small, privately held companies hoping to make a name for themselves. They include DeFi Mobile, Fring, Gizmo5, Sipgate and Truphone.
One advantage that these new companies have in competing with established VoIP services like Skype and Vonage is that old-style Internet calling required users to be sitting in front of a computer or hooked up to a laptop to make calls. Mobile phones with Wi-Fi chips free them from their PCs.
Ivan Domaniewicz, a commercial airline pilot with homes in Miami and Barcelona, recently switched to DeFi Mobile from Skype. His $40-a-month DeFi plan gives him unlimited Internet calls, voice mail and phone numbers in Argentina and Spain that are automatically transferred to his Nokia phone.
"It's really helped me keep in touch with my family and friends in Argentina and Spain," said Domaniewicz, who shuttles between the United States, Japan, Europe and the South Pacific.
"What's nice is that I don't have to take my computer out and start Skype-ing to talk to them. I just turn on my phone," he said.
Jeb Brilliant, an event planner from Long Beach, California, reduced his monthly AT&T plan to 700 minutes from a more expensive unlimited access plan after he became comfortable using mobile VoIP.
He uses Truphone, which charges 6 cents a minute to call landlines in most countries and 30 cents a minute to call mobile numbers. It also sells bundles of minutes that are discounted over its à la carte rates.
Brilliant has tried other mobile VoIP services and said that the technology could sometimes prove more reliable than cellphone service. When a family friend recently went into labor, he found himself making phone calls via a Wi-Fi network at the hospital.
"You can get it in places where there is no cellphone reception," he said.