Yes Jan,
I'm afraid they do content sniffing.
All ports forward well, but as soon as Remoterig's SIP is transferred, ports are dropped.
Reason: the telecom market in NL is becoming rather "nasty".
I also have to stay with this ISP for a year before I can change contract, and even after that no guarantee other ISP's do not sniff (they will never tell)
I also thought about "SIP in disguise" but I don't know how smart they sniff :-)
If you would like to do a pilot, would be more than happy to assist!
73
Paul
PD0PSB