Hi We are sertup on a version 12 with SIP-32G from Yealink latest firmware. using sip trunk, we dial out and after around 10 minutes we no longer hear the other end but they can still hear us. this is not happening on each calls. We have now installed a dsl loop from our sip trunk provider and we still have this issue. we are connected using a cisco ISA-500 with sip alg disabled. any ideas ?