Make an App and cloud based phone system that instructs humans to 'press 1' to connect call. (Look at image)

If the following summary is confusing, you can also view the image I have attached for a visual demonstration for better understanding. You can view the image here: [login to view URL] The Basics of the APP: 1) voicemail is forwarded to an external number. 2) the forwarded voicemail number is an external CLOUD / VOIP external programming phone system like Twilio, or SIP or you tell me what you recommend. 3) Call comes in, all calls not on contact list or "white list" are Declined and sent to voicemail. 4) call goes to voicemail (the VOIP), the caller must listen to a .mp3 that explains the caller "must press 1 to connect", 5) when the caller "press 1" then a message will play "stand by while your call is connecting" 6) then a message will be sent to the APP notifying to put caller on "white list" (maybe through text message) comes that says "the caller has pressed 1" 7) the app must listen for this message or alert, then add the number to the 'white list' 8) The app will send a signal back to the VOIP saying the caller is on "white list" 9) the voip will then forward the call back to the original number and it will go through because it is on 'white list' The app must: A) Be able to program phones to use call forwarding for voicemail B) Block (decline) calls automatically that are not in Contact List or White List. (or added to black list) The app "Call Blocker" does this C) Receive a message sent from VOIP system if the caller has "pressed 1" D) Add the number to the "white list" allowing future calls to pass through. E) Send a signal or message back to VOIP, allowing the call to continue. F) User of App should be able to add calls to "black list" and "white list" manually. G) The app must have a clean UI The Cloud/VOIP must A) Play a sound file as a message to the caller that user can customize / personalize B) allow 'press 1', press 2 commands B) communicate with APP either through text message or other C) receive communications from app to allow to send the call Extra: A)The VOIP must also have other options such as "press 2 to leave a voicemail" which will get transcribed and sent to the User. B)Another example would be to "press 3 to connect to receptionist" (These are customized by the user) C) If it is possible to have the APP customize instructions to the cloud, for instance, a custom sound file for the message, and custome phone tree (press 1 to connect, press 2 for voicemail) I will need all source code files and completed work. I would like to ultimately get the app on the playstore so the UI must be good too. Any advise is appreciated. I want the app to be perfect and sometimes small changes are needed, i reserve the right to add small features without being upsold by the freelancer - if the work is good, I will pay and pay extra, if this work is bad, i will not pay. This is a rough draft example so changes might be made, so bid accordingly.