It’s a rather new phenomenon, but we are seeing the beginning of a shift to making more voice calls on WiFi networks than on cellular networks. As Americans have become more conscious about making data connections on WiFi they have opened the door to using WiFi for their voice usage.

The trend of using WiFi for voice, as it matures, could really shake up the cellular industry. The AT&T and Verizon cellphone plans are among the most profitable products sold by any corporation and that makes them a target for competitors, and a place for consumers to save money.

It’s funny how the industry has changed so much. I remember twenty years ago going to state commissions and asking, and being rejected, for $2 rate increases in local telephone rates because the regulators feared that people couldn’t afford to pay it. And yet a decade later families went from having a $30 home phone to paying three and four times that much for cell phone plans.

There are several companies that have been selling WiFi calling for the last few years. FreedomPop, which started in 2012, offers a product that uses a network of over 10 million hot spots in places like McDonald’s or Starbucks. FreedomPop’s phones will automatically join WiFi networks much like a normal cellphone automatically connects to a cell tower. Their rates are really low and for $5 a month a customer can have a WiFi-only plan that connects to the network of WiFi hot spots. There are other slightly more expensive plans that use a combination of WiFi hot spots and Sprint’s cellular network when WiFi isn’t available.

Republic Wireless has a similar set of products. For $5 a month, customers can make calls or connect to the Internet solely over WiFi. For $10 a month, they can use both WiFi and Sprint’s cellular network. Republic Wireless has developed a technique that lets customers roam between hot spots (but this roaming is more suited to walking than driving in a car).

Scratch Wireless has an even more aggressive plan and using their WiFi network for voice, text, and data is free as long as you buy their $99 Motorola Photon Q phone. They then sell pay-as-you-go access to voice on Sprint’s cellular network starting as low as $1.99 per month.

These companies are growing rapidly. FreedomPop says it is doubling its customer base roughly every four to six months; Republic Wireless says its customer base is growing 13 percent a month. But both companies are still really tiny compared to the big carriers and are mostly catering to those who live mostly around WiFi and who are cost conscious. From what I can see, both companies get rave reviews from their customers.

Cablevision recently announced a WiFi-only plan for $30 a month for non-cable customers but only $10 for bundled customers. I don’t understand their pricing, which obviously is not going to be very attractive to non-Cablevision customers. Cablevision operates an extensive network of hot spots in New York, New Jersey, and Connecticut.

The real disruptor might be Google. They announced that they are going to be offering cellular phone plans and the industry seems to think that they will be WiFi-based. Certainly in the markets where they have fiber networks they could saturate the market with outdoor WiFi hotspots and offer a true competitor to cellular. Google has always said that they think bandwidth ought to be ubiquitous, and since they don’t own cellular spectrum, they are going to have to go the WiFi route and also make a deal for off-network minutes from Sprint or T-Mobile.

One also has to think that Comcast has their eye on this. They certainly are rolling out a huge WiFi network as they turn customer routers into public hot spots.

And so the phenomenon is starting to grow. The large cellular companies say they aren’t worried about this, but one has to think that in the Boardrooms they are keeping an eye on this trend. For now there are issues with using these products. One is data security as it’s fairly well known that public WiFi hot spots are loaded with danger for users. This has to be the case whether you are hitting a hot spot with a PC or a cellphone.

I know that personally I will probably stick to a bigger company plan. When I travel it is more often to out-of-the-way places than to big cities. And those kind of places generally have coverage of some sort by the big carriers, but are often uncovered by smaller carriers like Sprint and T-Mobile. I would not like to find myself in a small town for a few days with no cellphone coverage. Other than that travel, I work at home and could easily use my own WiFi rather than pay for cellular.

For the product to be competitive, it’s also going to have to be usable on the major phones being sold. Not having this product for the iPhone or Samsung Galaxy limits the target audience. For now the small carriers like Republic load their own proprietary software on the phones they sell to users. But as that turns into a downloadable app I could see this product picking up a lot of traction in cities.

AT&T and Verizon are right to not be worried about this today. But if you look forward a few years this could grow into a significant competitor to cellular. Which, even if it doesn’t mean a loss of a lot of customers for the big companies, will mean overall lower prices for cellphone plans. That is something they ought to be worried about.