Making a phone call and keeping it in the background

I have an app , that you can put numbers and then press a call button.
when I use Device.OpenUri(new Uri( string.Format("tel:{0}",viewModel.PhoneNumber))); to make the call, it is actually takes me to the calling page.
I would like to know what can I do in order to make it make the call and put it in the background without leaving the main app. Is that possible ?