Hi, I think almost everybody did it once: you call the pbx, the pbx hangs out, it calls back using the caller id, you type the number you want to dial using dtmf and the pbx calls the number for you. Such a way you can make a completely free call. Of course you should implement CLI whitelists and passwords to enhance security.
Unfortunately I don’t use this function since several years, I lost the code and I don’t really remember how I achieved it. Do someone has some code to share?