Hello I am based in Miami Florida
In the US we have strik law abou braking contract of IP (intellectual property ) so i wll not disclose your app to anyone
In your case check the app chat2talk it is VOIP based , since I have done an app like you need the app will take shorter time to do
I specialize in rapid Android apps development in the business education tools, and communication Machine to Machine (sometimes called internet of things)
Created hundreds of apps for satisfied customers and you can view few Demo aps a created to show capabilities:
Tools:
WI-FI Chameleon
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Communication:
Chat2talk
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Business:
wrBeacon
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I will be glad to work on your project
Let me know if you have any questions
Mickey