Merging calls on an iphone to speak to more then one person at once

[iphoneissue]

-When on a call to someone else you have the option to touch the " add call" button and add another person.

- Once i do this and then tap 'merge calls' to bring the two together it drops out????

does anyone know why this would happen?

[10000000000GB]

Is this on a business plan that you have paid for conference calls?