How to make multiple phone calls at the same time

Question

I have an application, where I'll be having between 10-100 minimum phone numbers on which i want to periodically (let's say once a week) make a missed call (about 20-40 seconds of ringing and then hanging up, using all numbers "at the same time").
I haven't tried any code yet but i already looked up how to make calls, missed calls etc. so I hope I know my way around this stuff a little bit.
Now you see if I'd do it by using simplest way, I'd have about one hour of my phone making these missed calls one after each other.
Is there a way to make these calls somehow overlap each other (make them all at the same time)? Because I looked up that I can't make a phone call in background and since we are using activity to start a call, if I immediately start call after previous one, I suppose since it's an activity it's gonna pause.

Answer 1

As far as I know, it's impossible to call different phone numbers simultaneously on Android and mobile operators do not let you do it either. If you really want to do it, you should use an API like Twilio to make all calls. However, if you're using the API, your own phone numbers will be used for calls, not the mobile phone owner number.

And if you want to know how to do it all at once, this is what threads are invented for! Assuming you have 100 phone numbers, use 100 threads to simultaneously call and hang them via API.