Incoming gsm call on symbian

[loki1@xxxxxxxxxxxx (loki1 at bezeqint.net)]

Hi. I'm using CTelephony api to monitor GSM calls. The problem
is that if i get gsm call while in pjsip call i can't hear GSM
ring, even though, i close pjsip call immediately. I'm using
pjsip 1.2 with APS. What can be the problem? 

Thanks in advance.