“That’s a whole car payment,” said Celozzi, a tailor who owns Hems While You Wait, in Hyannis. She regularly threatens her girls with the ultimate consequence — “I’m taking you off my phone bill” — but the overcharges keep coming.

“It’s stressful when you’re a single mom,” she said.

Even as giddy consumers await delivery of  their new ­iPhone 5s, a less happy side of mobile life is emerging. Think of it as “iStrain,” or wireless-induced financial anxiety.

Once discretionary, cellphones have become a fact of life for the vast majority of Americans — as have the bills consumers incur for plans that cover calls, texts, and data.

Nearly half of Americans with mobile phones pay $100 or more per month, and more than 1 in 10 spend at least $200 a month, according to a September survey by CouponCabin, conducted by Harris Interactive. That’s a major cost for those struggling to make ends meet.

“People say ‘I have to pay my phone bill, I can’t pay the doctor,’ ” said Jay Gonsalves, president of the Action Collection Agency of Boston, in Middleborough. “People put cellphone bills right up there with paying the rent.”

It’s the same story at American Consumer Credit Counseling, a Newton-based nonprofit. More than half of the agency’s 20,000 clients tell counselors that their wireless-phone bills are adding to their woes.

“Wireless bills are a significant problem, especially once you add in text and data,” said Katie Ross, the firm’s education and development manager, “but people don’t want to let go of staying connected.”

So many consumers complained about unexpected fees and increases in charges that in 2010 the FCC proposed regulatory action for wireless carriers unless they agreed to voluntarily alert consumers before (and after) they exceeded their text, voice, or data limits, or incurred roaming charges. The new rules go into effect in October.

The action follows a 2010 survey by the agency that found that one in six mobile device users had experienced “bill shock,” with 23 percent of those users facing unexpected charges of $100 or more. Some totaled thousands of dollars.

With an ever-increasing percentage of Americans owning mobile phones — use by adults is now at 85 percent, according to the Pew Internet and American Life Project— cost has become a matter that concerns even the White House.

“Our phones shouldn’t cost us more than the monthly rent or mortgage,” President Obama said in April.

So far, the average wireless bill doesn’t exceed most rents, or come close. But as more people get smartphones, costs become a bigger issue. Thirty-five percent of people with a household income under $30,000 a year now own a smartphone, according to Pew. That’s up from 22 percent in that income category in May 2011.

Once smartphones were only for business, but today even grade-schoolers are walking around with iPhones and BlackBerrys.

Figures from the wireless industry association, CTIA, show that the monthly cost of service per wireless device has dropped slightly. The average was $47 a month in 2011, for example, compared with $47.21 per month in 2010, and $48.16 in 2009. But with more households paying for multiple devices, many consumers end up paying more.

And, of course, some people are paying much more. Prices for the new iPhone 5, for example, start at $199.99, with a contract, and can go over $800 for an iPhone 5 without a contract.

Because the iPhone 5 is a different size than previous ­iPhones, new accessories and chargers will likely add $100 or more to the price.

Additionally, the larger screen size could encourage more data consumption, experts say, and with it, the need for a larger, more expensive monthly packages, or pricey overage charges.

“We’re the frogs in the proverbial pot,” said Jason Alderman, a senior director at Visa Inc., who runs the company’s global financial literacy directive. “We keep adding costs and the temperature keeps going up, but we don’t realize the water is now boiling.”

Not only can a phone be a large one-time purchase, Alderman said, “but it becomes a permanent line item for the rest of your life, and one that will likely grow,” as data and text plans that initially seem fine soon feel woefully inadequate.