AT&T and Verizon Wireless today announced that both carriers are working on enabling VoLTE-to-VoLTE calls between their subscribers.

“Interoperability of VoLTE between wireless carriers is crucial to a positive customer experience,” Krish Prabhu, president of AT&T Labs and Chief Technology Officer at AT&T, said in a statement. “We continue to work with others in the industry on similar collaborative arrangements and hope to see similar collaboration across the industry in the near future.”

The carriers anticipate VoLTE interoperability between AT&T and Verizon will be available in 2015. Both carriers had their initial VoLTE launches this year.

AT&T and Verizon have engineers testing in lab environments and will then move on to field trials. Both companies have been collaborating with GSMA on the initiative. GSMA is in the midst of its 2020 program which is pushing global mobile operators to move to all-IP network models.