Dear sir,
We have done similar types of task that you described.
We can do the job with api or push notification message or i need more explanation on [login to view URL] we can show webview and audio part will test after full requirement in my hand.
Sample of my previous works are as follows:
Alles Car: Amazing android apps for car users that helps users for hiring a car.A driver from driver app can response users call for [login to view URL] these app i have use push notification and alarm. [login to view URL] [login to view URL]
More Samples Apps links:
https://www.freelancer.com/projects/Android/Android-APP-7401011/
[login to view URL]
[login to view URL]
[login to view URL]
Uses Technology: Git,Svn,Eclise,Android Studio,Json,Gson,Volley Facebook SDK, Twitter, Googleplus ,Google Map API,GPS,NFC,Google Earth, Apk Expansion,Payment Method(zooz),Audio Player,Video Player, AdMob,AChart Engine,Utube api,Google analytics api,Mail chimp api,Google GCM api.
Thanks
Yours truely
Mobile Apps Innovator