The first handsets running Mozilla’s "Boot to Gecko" (B2G) software will be available in Brazil on Telefonica Vivo’s mobile network.
Brazilian tech blog Ztop broke the news but had no details about which firm will make the handsets.
Announced in July 2011, B2G aims to be an open rival to Google’s Android.
The Mozilla Foundation is best known for its Firefox browser that adheres strictly to official standards for writing and viewing web pages.
B2G was started as a way to bring the same discipline to mobiles and give people more control over what their phones do and the applications they run.
It gets the name "Gecko" because that is the part of Firefox that decides how to display pages in a web browser.
Speaking at a press conference in Sao Paulo, Gary Kovacs, chief executive of Mozilla, said this openness would make a difference to the way applications on phones operate.
B2G aimed to make apps more like webpages and able to share data and links, he said. It did this by basing everything on the latest web standard known as HTML5.
No details were given on who would make the handsets that Telefonica Vivo was planning to offer to its 90 million customers. It said the phones would cost about the same as existing feature phones.
No specific date for the launch was given but Telefonica said it should happen at the end of 2012 or in early 2013.