SIMI VALLEY– When AT&T started slowing down the data service for his iPhone, Matt Spaccarelli, an unemployed truck driver and student, took the country’s largest telecommunications company to small claims court. And won.

His award: $850.

Pro-tem Judge Russell Nadel found in favor of Spaccarelli in Ventura Superior Court in Simi Valley on Friday, saying it wasn’t fair for the company to purposely slow down his iPhone, when it had sold him an “unlimited data” plan.

Spaccarelli could have many imitators. AT&T has some 17 million customers with “unlimited data” plans who can be subject to throttling. That’s nearly half of its smartphone users. AT&T forbids them from consolidating their claims into a class action or taking them to a jury trial. That leaves small claims actions and arbitration.

Late last year, AT&T started slowing down data service for the top 5 percent of its smartphone subscribers with “unlimited” plans. It had warned that it would start doing so, but many subscribers have been surprised by how little data use it takes for throttling to kick in — often less than AT&T provides to those on limited or “tiered” plans.

Spaccarelli said his phone is being throttled after he’s used 1.5 gigabytes to 2 gigabytes of data within a new billing cycle. Meanwhile, AT&T provides 3 gigabytes of data to subscribers on a tiered plan that costs the same — $30 per month.

When slowed down, the phone can still be used for calls and text messaging, but Web browsing is painfully slow, and video streaming doesn’t work at all.

AT&T spokesman Marty Richter said the company will appeal the judge’s ruling.

“At the end of the day, our contract governs our relationship with our customers,” he said.

AT&T area sales manager Peter Hartlove, who represented the company before Nadel, declined to comment on the ruling. He argued in court that his employer has the right to modify or cancel customers’ contracts if their data usage adversely affects the network.

Companies with as many potentially aggrieved customers as AT&T usually brace themselves for a class-action lawsuit. But last year, the Supreme Court upheld a clause in the Dallas-based company’s subscriber contract that prohibits customers from taking their complaints to class actions or jury trials.

Arbitration and small-claims court cases are cheaper and faster than jury trials, but they force plaintiffs to appear in person and prepare their own statements. In a class-action suit, the work can be handled by one law firm on behalf of millions of people.

That means thousands — and possibly hundreds of thousands — of people who feel abused by AT&T’s policy could seek to challenge the company, one by one, in arbitration or small claims court. The customer contract specifies that those who win an award from the company in arbitration that is greater than the company’s pre-arbitration settlement offer will get at least $10,000. Spaccarelli picked the same amount for his claim, though AT&T’s stipulation about a minimum award doesn’t apply in small claims.

Nadel looked instead at the remaining 10 months in Spaccarelli’s two-year contract with AT&T and estimated that he might pay $85 a month on average for using additional data. AT&T charges $10 for every extra gigabyte over 3 gigabytes.

Nadel said it’s not fair for AT&T to make a promise to Spaccarelli when he buys the phone while burying terms in his contract that give the company the right to cut down data speeds.