The feature that you need is called voice broadcasting and luckily there are applications and online services that can do this for you. I've look on various websites and it appears that one reliable service is DialMyCalls. The service got some reviews on LifeHacker which means it's pretty important and reliable.
Remember that you won't have the possibility to do this for free. Access the link posted below to reach their website: https://www.dialmycalls.com/