Connect call when the called/receiver side gives permission

How do I allow connection of the call , allow start of conversation only when the received person gives permission through a DTMF?

Which flag in Dial() will help do this?

Have you checked all the options for the dial command ?, if so you will notice there is not an specific flag to complete this task. But this task is posible to complete, and there are one million ways to do it. and some flags seems to be useful like . M( macro^arg ) , anyway I did it by using
localchanel, originate command , channelredirect and bridge()