Choppy sound

I am running asterisk 10.2.0.
I have iax and sip clients and Gtalk channel to PSTN.
I also have some iax clients on the iphone and ipod.
The client is called IAX dialer.
When Ipod client calls any other client (over wan or lan) the voice quality is great.
callflow is:
ipod iax client > asterisk > sip client or iax client or iphone client

this proves that iphone and ipod clients work fine

Now, if any client calls PSTN through gtalk channel all works great.
But if ipod or iphone IAX client calls PSTN through gchannel the receiving audio on PSTN is choppy.
It could be QOS or some other network issue, but if other clients work fine something is going on.

Is it possible that if specific client stream (IPOD or Iphone) is mixed with Gtalk the voice has issues?
I tried also direct sip provider to eliminate gtalk channel but same issue?

Any ideas?

i installed different iax client and it works, so i assume client has some issue.