The seven largest U.S. phone companies, representing more than 95 percent of the market, lost a combined 52,000 subscribers from contract-based plans in the January to March period, according to a tally by the Associated Press. The companies have a combined 220 million devices on such plans, accounting for about two-thirds of the total number of devices.

Since nearly every adult, and many children and teenagers, already have phones, there’s little room for growth anymore. But subscribers are also flowing to cheaper, no-contract plans, which showed an increase of at least 2 million. That figure, however, is down from more than 5 million in the same quarter a year ago.

The industry is also adding millions of non-phone devices, like smart energy meters. These so-called “machine-to-machine” connections usually carry very low monthly fees, on the order of a few dollars per month.

For example, AT&T subscribers on contract-based plans pay an average of $64.46 per month, while other AT&T customers pay an average of $11.52 per month.

T-Mobile’s report comes on the last day of the U.S. cellphone industry’s annual trade show in New Orleans. At the show, companies talked about various ways of boosting their business outside phones. For instance, AT&T launched a home security and automation business, and the head of its wireless business, Ralph de la Vega, said the company is getting closer to launching family data plans, which would allow the sharing of one “bucket” of data among various devices and family members. That could encourage people who already have a smartphone to get a tablet with data service as well. Verizon Wireless has already announced that it is introducing such plans this summer.

The first quarter is a seasonally weak one for contract-based plans, and the industry is likely to show some subscriber additions for the whole of the year. But the gains will be spread unevenly over the phone companies. For the last year and half, the four nationwide phone companies have added or lost subscribers in order of size: Verizon Wireless, the largest, has gained the most, followed by AT&T Inc. Sprint Nextel Corp., No. 3 in size, has mostly lost subscribers, while No. 4 T-Mobile has done so consistently. That poses a conundrum for regulators who want to preserve vibrant competition in the industry.

AT&T launched a major bid to consolidate the industry last year by striking a deal to buy T-Mobile for $39 billion, but the project was scuttled by regulators who said it would reduce competition and raise prices for consumers. On Wednesday, Bloomberg News, citing anonymous sources, reported that T-Mobile was in talks to buy MetroPCS Communications Inc., the fifth-largest cellphone company in the U.S. However, the combination would be difficult to manage, since the companies have incompatible networks. Branding could pose a challenge too: T-Mobile wants to appeal to business customers, while MetroPCS sells almost exclusively to low-income, urban households. Acquisition talk surrounding MetroPCS surfaces from time to time, but no deals have resulted.

The AP’s tally of subscribers excludes some contract-based machine-to-machine connections reported by T-Mobile. The company also added 435,000 prepaying subscribers of all kinds in the quarter, which was the best result in more than two years for that category. T-Mobile credits its new prepaid monthly plans with fast “4G” data service for the increase.

Overall revenue at T-Mobile USA, a unit of Deutsche Telekom AG of Germany, fell 2 percent from a year ago.

In addition to handing over spectrum licenses, AT&T gave T-Mobile $3 billion in cash, which will help finance the upgrade. T-Mobile plans to have the network live next year, covering 75 percent of the 25 largest cities.

Sweden’s Ericsson is one of the main suppliers for the LTE networks of Verizon Wireless, AT&T and Sprint Nextel Corp., along with Alcatel-Lucent SA of France.

For Nokia Siemens Networks, a joint venture of Finland’s Nokia Corp. and Siemens AG of Germany, the T-Mobile order represents a new chance to get into the U.S. market for network equipment. It got a $7 billion order from Harbinger Capital, a hedge fund, to build a network for its startup, LightSquared, but that project appears moribund because regulators concluded it would have interfered with GPS navigation.

T-Mobile USA is making the announcement on the first day of CTIA Wireless, the U.S. cellphone industry trade show, in New Orleans. The company is the fourth-largest wireless carrier in the U.S., with 33.2 million devices on its network. It’s a subsidiary of Deutsche Telekom AG of Germany.

Steven Winoker, an analyst at Sanford Bernstein, said about 23 percent of U.S. homes have security systems, so there’s plenty of room to grow. Even fewer have automation systems for controlling appliances, lights, heating and cooling.

The biggest player in the field is ADT, but it has only 25 percent of the market. Many smaller companies make up the rest, according to Winoker.

It’s a very profitable business, Winoker said, but it’s not big enough to significantly affect the earnings of a company of AT&T’s size even if it’s successful, given that it’s a relatively small market.

AT&T’s technology comes from Xanboo, a company it bought in late 2010. Its central control panel can connect wirelessly with cameras, thermostats, appliance controls, lights and sensors for doors, windows, smoke and carbon monoxide. Through the panel, home owners can then control their home from their cellphones.

It’s highly recommended that the control panel is connected to wired broadband, but it doesn’t have to be service through AT&T, said Glenn Lurie, AT&T’s president of emerging devices. As a backup, the panel can connect to AT&T’s wireless data network.

AT&T didn’t say what its services would cost.

AT&T made its announcement on the eve of the U.S. cellphone industry’s annual trade show, which starts Tuesday in New Orleans.

The added computing power will be put to use in the S III’s expanded voice-command features. When the phone screen is off, owners will be able to “wake” it up by saying “Hi, Galaxy.” They can then give further spoken commands. When Apple launched the iPhone 4S last year, it also made advances in voice recognition a central selling point.

Samsung will sell a pad that charges a phone placed on it, with no need to connect a cable. Palm Inc.’s last smartphone had a similar feature when released three years ago, but it never became popular.

Samsung said the phone will go on sale in 145 countries with 296 phone companies, making it the company’s biggest launch so far.

In the U.S., Japan and Korea, the phone will use fourth-generation, or 4G, networks for faster data downloads. Samsung didn’t say which carriers would sell it, but the previous Galaxy model was sold by all four national U.S. wireless carriers: Verizon, AT&T, Sprint and T-Mobile.

Samsung doesn’t release phone shipment figures, but most analysts believe its smartphones outsold Apple and its 35.1 million iPhones in the January-to-March period. Canaccord Genuity analyst Michael Walkley believes Apple and Samsung together accounted for virtually all the profits in the phone industry in the first three months of 2012, with three-quarters going to Apple by virtue of its singular focus on the high-priced iPhone.

Samsung and Apple have a complicated relationship. They’re rivals in the smartphone and tablet-computer markets and fight each other in court over patents. But Samsung is one of Apple’s largest suppliers of chips and displays, and Apple is one of Samsung’s largest clients.

The Galaxy series debuted in 2010. The screen size has increased with each version: The Galaxy S had a screen that measured 4 inches diagonally. It was followed by the S II, at 4.3 inches.

The S III screen has a 4.8-inch screen. Meanwhile, the iPhone screen has stayed the same size, at 3.5 inches, but the recent models pack more pixels into the screen, for a sharper display.