ah, so you mean the double call back.
yes, "pinging" the phone number with another number, so PINGING actually the CALLBACK number with another phone is fast and simple and doesn't cost anything,

but, running the RING AROUND, using a double call back is only trick the first or second time, after that it just works.

Call your CALLBACK number with the RIIING phone, and hang up. no charge.
phone rings, answer the call, that is riing, hang up. no charge, since you haven't made a call at all technically.

phones rings a second time, answer, that is your callback providor calling. Answer the call and type in your number to call and you are connected. If you are connected then you pay for that call, but if you are not connected, busy, etc, or just hang up, then there is no cost.