I am looking for an IAX provider in EU, preferably with folks that speak English. After requests to 5 different providers and no responses back I have turned to this board. We will be averaging 6000 calls per hour.
Where in the EU? Have you tried: http://www.voiptalk.org/products/configuration-of-iax-trunk-with-asterisk-pbx-for-use-with-voiptalk-setup?
Or even voipon.co.uk/. They support IAX and are very helpful. I used an IAX trunk from them for about 300-500 calls per day.
6000 calls an hour is a heavy load. If they are outbound, the better ITSPs may not want to touch you. I suspect you actually need to find an ITSP who can handle your traffic volume and calling pattern, then worry about choosing between IAX and SIP.