Attempting to build a Bitcoin-integrated global telephone system app

I am trying to build a Bitcoin-powered VoIP virtual phone exchange app for encrypted call routing, forwarding and redirecting virtual phone numbers of all countries that will be integrated with a blockchain.info/api wallet of ours and corresponding user wallets by hooking into Blockchain.info's API. A call can only be made if adequate Bitcoins are available with user's wallet to initiate the call for a minimum time slab(1st slab) of say 10 minutes. This minimum slab rate will be automatically deducted on connecting a call successfully by sending out the payment from the users' wallet automatically without requiring any re-permission and only after 5 confirmations. And moreover next slab's amount should be available and blocked for securing applicable call charges that's anticipated, should the caller or call receiver extend the duration of the call beyond the first slab. On the backend I am trying to integrate FreePBX (freepbxhosting.com) with Twilio elastic SIP trunking for call forwarding and routing. I do need help here too.