A small Phoenix company is taking on some of the giants in the cellular phone industry, claiming that many companies are copying its patented invention for pay-as-you-go cell phone service.

Freedom Wireless Inc., a four-person operation, has sued at least a half-dozen companies — including Cingular Wireless LLC and Verizon Wireless — in the past 18 months for allegedly infringing on three patents involving the prepaid cellular phone concept.