With some wireless carriers reporting historic growth in the third quarter, it is hard not to wonder how long the momentum can last.

With 928,000 additions, AT&T Inc.'s postpaid phone subscribers in the third quarter were nearly double analyst predictions and at the highest rate in nearly 10 years. T-Mobile US Inc. reported adding 673,000 postpaid phone lines, the highest third-quarter account growth in nearly seven years. Verizon Communications Inc. added 429,000 postpaid phone net subscribers, up more than 50% from the prior year.

A combination of factors should be considered to understand why postpaid adds continue to rise, analysts say, pointing to upselling, low churn and Americans' desire for additional lines. Analysts believe these factors will help mobile providers continue reporting strong additions for quarters to come as wireless line additions outpace population growth.

Upselling is one of the main forces driving postpaid adds, according to Kagan analyst Lynnette Luna.

"There is a big push among both AT&T and Verizon to upsell their lower-paying subscribers," Luna said in an interview. "Verizon, in particular, is being very aggressive about getting its existing customers onto premium unlimited plans with smartphone promotions that it frequently rolls out and then pulls back. Its ability to package a lot of exclusive streaming services has been a strong selling point."

Subsidies and promotions

Cable operators Comcast Corp. and Charter Communications Inc. have also had strong wireless adds, and they will have to keep offering plan subsidies for mobile devices to keep up with incumbent wireless operators, Wave7 analyst Jeff Moore said.

"Wireless carriers are pushing high-end unlimited plans with streaming, which could be impacting video additions at cable companies as more people decide to depend solely on streaming," he said.

AT&T has been offering steep subsidies on devices like Apple Inc.'s iPhone 13 Pro or Google LLC's Pixel 6 Pro to both new and existing customers, which has helped keep churn low and led to higher net adds.

"AT&T's promotions remain by far the industry's richest," MoffettNathanson analyst Craig Moffett wrote in a research note.

But AT&T executives say it is more than just promotions driving AT&T's success, pointing to simplified rate plans and optimized distribution channels.

"We know, based on these metrics that we see, that we're adding high-value customers and don't believe that this is driven uniquely by any kind of subsidy or extra cash flow that happens to be in the marketplace of the general market," said Jeff McElfresh, CEO of AT&T Communications.

T-Mobile is crediting its expanding service area for record postpaid adds.

"Smaller markets and rural areas are already contributing about one-third of our new accounts and brand equities are up across the board," T-Mobile CEO Mike Sievert said during the company's earnings call.

Government aid

Aside from company sales strategies and expanding networks, government spending programs are also helping elevate phone additions.

Moore said money pushed out by the government during the pandemic could explain high pospaid adds, even if indirectly. "The Emergency Broadband Benefit Program gave families subsidies on internet services, which in effect may have helped many people afford their wireless plans," he said.

Recon Analytics analyst Roger Entner said lower-income Americans who would have typically given up their phones or considered a prepaid device during an economic crisis may have used emergency funding to continue paying for postpaid services.

"In 2008, postpaid adds collapsed while prepaid expanded rapidly, but both the Trump and Biden administrations have cushioned the financial impact of the pandemic more than any other administration during a financial crisis," Entner said.

Multiple lines

Cell phones are more integral to the American lifestyle than ever before and changing consumer trends could help wireless providers maintain strong postpaid subscriber numbers for the long term, said Luna.

"People are buying phones for their children at earlier ages than previously, and some people are buying more than one line of service," Luna said.

Moore said more people have experienced the benefits of having two lines, and since wireless companies are offering additional lines at low costs, people are willing to buy. "A lot of people just enjoy having two lines. Whether it's for business or even criminal reasons, a lot of people are willing to pay money to have more than one voice line," he said.