Sopock said:
maybe softphone is using server name like sip.orange.es
You aren't using a VoIP provider directly (as I understand it), you are using a router with some sort of a gateway built in, so the use of URLs is probably not an issue.. What IP address is your 3CX server using? Did you give it a fixed IP on the network? I'm assuming that the "box" acting as a Gateway, is also the router/DHCP server? Did you do any port forwarding on the router portion that may be interfering with where port 5060 is routing to?
You may need to provide more detail about how you have you network set up. is the router and gateway using the same IP (192.168.1.1) ?
Have you done any searches on the net using the make/model of the device you are using , along with "3CX", to see if anyone else has has success in using it? It may very well be some simple setting that is preventing it from working properly, but there may be others out there (in Spain), that have tried this before. They may have posted their results if you do some searches.
I just did a search for "Livebox" and the device that came up would seen to indicate that it has an RJ11 socket for an analogue phone. This would mean that it is an ATA. Are you trying to bypass the built in ATA and register directly with the provider?