Linphone Android client http://www.linphone.org with the custom specifications.
Linphone, Android, Java, Sonim XP7 with Push-to-Talk (PTT), NDK
Setup with Sonim XP7 smartphones with Push-to-Talk (PTT) button. Using communications with FreeSwitch proxy server. Rebranding the whole front end with company theme. Customizations of ASSISTANT and SETTINGS. Auto provisioning: server address, outbound proxy, and port hard-coded [Server option not available]. User login with username and password.