In recent weeks, the two big American phone carriers, AT&T and Verizon, have been talking big about Microsoft’s Windows Phone software. AT&T has been hurling loads of money at marketing Nokia’s Lumia 900 , a smartphone that runs on the Windows Phone operating system. And now Verizon, too, has revealed plans to aggressively promote Windows Phone 8, the next version of Microsoft’s software.

Fran Shammo, Verizon’s chief financial officer, said last week that the company wanted a third big player in mobile software to come into the picture, and it was going to throw Microsoft a bone.

“We’re really looking at the Windows Phone 8.0 platform because that’s a differentiator,” Mr. Shammo told Reuters after Verizon’s earnings report on Thursday. “We’re working with Microsoft on it.” He didn’t say when Windows Phone 8 handsets would be available on Verizon.

All the chatter about Windows phones is abrupt. Before April, Windows Phone 7 seemed virtually irrelevant to consumers, and American carriers were relatively quiet about the operating system. So why, suddenly, all the love and support for Windows Phone?

The answer is multifaceted: The carriers are tired of Apple’s calling all the shots, Microsoft offers a compromise, and everyone is watching with weary eyes what exactly Google will do with its purchase of Motorola Mobility.

Verizon and AT&T were very likely stunned by the iPhone’s blowout holiday quarter for both companies, said Tero Kuittinen, a mobile analyst and vice president of Alekstra, a company that provides services for people to manage their phone bills. In that three-month period, Apple sold a record 37 million iPhones, and the iPhone was the best-selling handset for both Verizon and AT&T.

Moreover, Verizon said that half the smartphones it sold were Apple’s. We’ll learn more from AT&T Tuesday when it reports its financial results for the first quarter, but Verizon clearly sees Apple as predominating over Google’s Android right now.

“There clearly is a danger now that iPhone is going to get a stranglehold of the U.S. smartphone market, and I don’t think operators are crazy about that,” Mr. Kuittinen said.

The implied threat of the iPhone’s continued success is that Verizon and AT&T are losing control of the customer billing experience. Apple not only controls the design of the hardware and software of the iPhone, but also the store for purchasing additional media. The more the iPhone succeeds, the less leverage the carriers have, Mr. Kuittinen explained. All they have is bandwidth.

And then there’s the question of what exactly Google is doing with its acquisition of Motorola Mobility, which is expected to be completed in the next few weeks. Owning a mobile hardware maker puts Google in the position to emulate Apple’s approach by controlling both the software and hardware design of an Android handset, thus gaining leverage over the carriers — a possibility that AT&T and Verizon can’t be thrilled about.

Amid the ferociously competitive and changing mobile landscape, Microsoft’s Windows phone software offers compromise. For example, Microsoft allows the carriers to preload some of their apps on the main screen of a Windows Phone 7 device. Microsoft will also feature apps made by its partners in its app store — customers of the new Lumia 900, for example, will see Nokia’s Drive app for GPS navigation prominently displayed in Microsoft’s Marketplace for apps. (At what point will Nokia’s getting close to Microsoft worry them as much as Google’s closeness to Motorola?)

For carriers, now seems like a better time than any to latch on to a third software system and see where it takes them.