Using app on Iphone How do we place on hold after answering?

Instead of Crickets They should be listening to our uploaded hold message, then re-answer?

Is there a secret code?

Our company uses T-Mobile business cell phones. Please help

We just want to answer phone call, which is forwarded to cells, talk, place on hold "they hear our already uploaded hold message play" re-answer, talk, hang up=SIMPLE