Require Linphone based communication app

I am looking for a skilled developer to create a Linphone based communication app that is compatible with both iOS and Android platforms. However Android is more concerned, iOS will be a plus factor. The app should have the following specific feature:

1. App will be a communication app where multiple users can talk.
2. There will be one admin who will initiate the call & there will have multiple users who can attend the call
3. Users cant make a call to anyone, they can just attend the call initiated by the admin.
4. It will be the case that not all users will be available when admin places a call, so users can come later & join that group call.
5. Admin can listen to all the users, but users will be able to listen admin only & not to each other.
6. User will have a push button, which until pushed, user can talk, as user leave that button, his mic will get muted. This is just to avoid extra noise at user's end.
7. Multiple users will be able to talk to the admin at same time, so it will be Admin's problem that how he will understand & communicate with them.

Android App is preferred, however if you can deliver a common app that can be for Android & iOS both, then your chance of taking the job will be high.

For above mentioned features, if you have used / worked on any other SIP based app then please let me know, we can explore other open source option also.

Layout will be sent to the awarded person.

Only experienced developer with Ubuntu & Linphone need to apply to save my & your time.

Thanks for reading above details.

Happy Bidding !