Prism Technologies makes money licensing its patents, and has taken many companies that use them to court. The company has also accused T-Mobile, Verizon and US Cellular of violating the same patents.
Sprint said it planned to pursue "post-trial motions" to contest the judgement.
Critics claim that the US patent system allows companies or "patent trolls" to acquire the rights to inventions and demand money to use them, without making products of their own. The US is currently debating ways to reform how it hands out patents for technology.