Hangup problems

I am new to asterisk, I have configured a basic asterisk pabx on my pc using fedora core 6, asterisk 1.4.19 zaptel 1.4.10 and wanpipe I am using a sangoma card with 2fxo and 2 fxs ports. I have 2 anolog phones for now. The problem is when an external pstn/pots call comes in and then hangs up asterisk wont hang up.
The problem might be the tone indications. We use an exchange called niax, apparently from Japan but i am unable to find out anything more about it.
For now i am using south africa (za) as the default location which is closest to my country, Malawi. and because traditional pabx’s work properly when za is used but is not working for asterisk. Could you help me find out more about niax? And if any country in indications.conf has similar tones?
Or could it be that i need to use only sip/iax phones for the asterisk pabx?
What else could be causing this problem?
please assist…

That problem will not be due to tone indications.

You need to find out what convention, if any, the Malawi PTT uses for release supervision and configure for that, if possible.

You may need to add a parameter to the dahdi/zaptel kernel driver, to optimise it for your country, as well as configuring dahdi/zaptel, at the Asterisk level, for the correct supervision type.

I don’t have access to analogue phone hardware, so I haven’t looked at this in great detail.

You may want to look at this: http://www.asteriskguru.com/tutorials/resolving_hangup_detection_problems_fxo_tdm_voicemail.html. It looks like the indication file may influence some hangup detection strategies.