BT is suing Google over claims that the Android operating system infringes on some of its intellectual property and patents.
BT said that it has commenced legal proceedings with the US District Court of Delaware.
"The patents in question relate to technologies which underpin location-based services, navigation and guidance information and personalised access to services and content," the telco said in a statement.
"BT's constant investment in innovation has seen it develop a large portfolio of patents which are valuable corporate assets. This is about protecting BT's investment in its intellectual property rights and innovation. It is a well-considered claim and we believe there is a strong case of infringement."
BT joins a long list of companies that have aimed lawsuits at Google and Android.
"With so many major patent holders asserting their rights, obligations to pay royalties may force Google to change its Android licensing model and pass royalties on to device makers," said patent expert Florian Mueller on the Foss Patents blog.
"Android already had more than enough intellectual problems anyway. Now Google faces one more large organisation that believes its rights are infringed.
"BT probably wants to continue to be able to do business with all mobile device makers and therefore decided to sue Google itself."