Most of SIP providers need different RTP settings.
With S series, you can't set RTP range as you want and I think it's a shame.
Why you are so restrictive ?
Maybe there is a workaround to do it by this way :
I don't know, but it would be interresting to handle this directly in the beautifull GUI.
In another hand, a SIP provider ask me if S series has RTP proxy capability and one of your colleage from the support team confirmed me it's not supported.
Can you do something ?