Hello,
I found a very interesting thing. If I retry the call after the 407 message (several times), it let me finally make a call. And if I insert 100rel = no it almost let me call in the first attempt (not always). I can make them even if the INVITE has the Route field in the headers
Is a very weird stuff what is doing the proxy, but at least I can make calls with a simple RetryDial. So the final endpoint config looks like this:
[sfr-out]
type = endpoint
transport = transport-udp
context = from-sfr
outbound_auth = auth_reg_residential.p-cscf.sfr.net
from_domain = ims.mnc010.mcc208.3gppnetwork.org
from_user = +33666666666
allow=!all,g722,alaw,ulaw,gsm
aors = sfr-out
outbound_proxy = sip:residential.p-cscf.sfr.net\;lr
100rel = no
allow_subscribe = no