It seems that it's the case here. We can access BIS by wifi only through their hotspot or their Livebox (Orange router) like UMA.
But there's something remaining i can't understand. When i got my new BB (I bought it to a jobmate) the bis wifi connection was ok and i could get my mails like this but no UMA which is normal because in France it's offered by Orange with their livebox.
I wiped out the device and then BIS through wifi had never worked again except through the Orange router.