Motorola, Siemens and Sony Ericsson today announced the first joint interoperability tests of push-to-talk over cellular (POC) technology. The companies hope the tests speed the delivery of compatible POC to network providers. They are targeting second quarter of this year for the delivery of the first interoperable POC products and solutions. Interoperability is seen as the key to expanding POC to Europe and Asia, Motorola said. The first POC technical standard was submitted to the Open Mobile Alliance in August 2003, and Motorola, Siemens and Sony Ericsson are promoting a final version of the standard through the OMA, Motorola said.