The foundation is a non-profit that provides financial backing for several top Linux hackers, including Linux creator Linus Torvalds, to work on the kernel.
A foundation statement said AT&T's move followed the donation of a few million lines of ECOMP code, as well as the new Open Network Automation Platform (ONAP) Project based on production-ready code from AT&T and OPEN-O contributors.
Chris Rice, senior vice-president of AT&T Labs, would join the foundation board.
“So, it was a natural decision for us to join The Linux Foundation. SDN is helping us meet performance, capital spending and efficiency goals and we expect continued benefits.
"But more so, we recognise that the open source community accelerates innovation. We’re excited to work with The Linux Foundation and its members to promote a globally accepted platform for SDN and NFV technologies.”
Foundation executive director Jim Zemlin said: "AT&T’s membership and the launch of the ONAP Project kick off a year that promises to be pivotal in open networking.
“We welcome Chris to our board of directors and look forward to close collaboration with AT&T to rapidly advance SDN and virtual network functions.”
Linux Foundation Platinum members include AT&T, Cisco, Fujitsu, Hitachi, Huawei, IBM, Intel, Microsoft, NEC, Oracle, Qualcomm Technologies and Samsung.
AT&T has collaborated with open source communities on OPNFV, the Cloud Native Computing Foundation, Open Container Initiative, OpenStack, ON.Lab, Open Networking Foundation and the OpenDaylight End User Advisory Board.