Break of connection for one party

I use Asterisk 1.2.1.
I Do IVR for pre-paid card system. When the caller has passed authorization and already talks to the called number, whether it is possible to make so that by pressing, for example, *0, calling interrupted communication with caused number, but did not interrupt communication with IVR.

It is necessary, that it came back in the context and could call still somewhere. It would be convenient: it is not necessary to dial anew up to IVR and to pass authorization anew. I try to edit file features.conf
disconnect => *0
and in extensions.conf
exten => 1236,5,Dial(SIP/${DNID2}@cisco5350,20,hH)
The call comes and leaves Asterisk through SIP channels.
In cmd Dial() I try keys:
h: Allow the callee to hang up by dialing *
H: Allow the caller to hang up by dialing *

If there is a key h, that to whom have called can interrupt conversation,
pressing and if H that calling can interrupt conversation. But after such interruption, are dumped both caller and called, i.e. the call destroy and the further transition on priorities which are registered in a context does not occur. I do not understand, this feature if it is possible to hang up simply what for is made.

exten => 1236,1,Wait(1)
exten => 1236,2,Answer()
exten => 1236,3,SetLanguage(ru)
exten => 1236,4,AGI(agi-card.agi)
exten => 1236,5,Dial(SIP/${DNID2}@cisco5350,20,hH)
exten => 1236,6,Playback(blablabla)

Up to 6 priorities does not reach at pressing *0.

Please provide your config related to your h extension. Using your current dialplan; how do you plan on terminating the call mid-session when the customer has run out of credit?