For SIP2SIM we register to VoIP services. The contact we register is what is used for the server to make a call in to us to call the phone with the SIM. The contact we used is of the format sip:[user]@[ip];line=[id] for example sip:fred@81.187.30.111;line=654478631245645613. This is a completely valid SIP URI and is the format used by many SIP phones. The line= part allows us to validate the incoming calls as from that registered carrier and is a very long random number. Sadly at least one carrier is incorrectly strippign the line= part of the URI. This is wrong, and means we cannot identify the call and so the call fails. We are making a work around for this. Obviously we should not have to, but we think we have come up with a way to do things that will work and be valid. We are changing the contacts to be of the form sip:[user]@[host] where the host part starts with a long number using a wildcard DNS record. We do not expect any problems with this, but if there are any, please let support know ASAP as we can easily change back.