A judge in California has ruled that Sprint Nextel’s early termination fees are illegal and said the wireless operator should pay back $18.2 million in collected fees to consumers, a decision that could help sway decisions on similar cases throughout the country.

The preliminary decision released earlier this week is a major blow to Sprint and to other phone companies in their battle to defend themselves against angry consumers who say the fees imposed on them when they leave the companies’ services are unlawful.

Verizon Wireless, which was also being sued in California, has already settled its case, agreeing to pay $21 million to settle all claims against the company. And after the decision against Sprint, there’s a chance that cases against T-Mobile and AT&T could also be settled.

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