Well, since no one was able to help me, and I've eventually managed to fix this, I'll add my solution (and problems) in this post.
So, I needed to connect to a Soap Service using WSSE. Not with a user/pass auth in it, but with a client certificate, a binary security token and such wonderful things.
First, I needed to make a p12 certificate file, using my client certificate (with the cert chain) and my private key (used to request the client certificate).
Next, I needed to convert the p12 file to a BASE64 encoded pem file.
Finally, in the soap_client constructor, you need to add "local_cert" and "passphrase" in the options part with the full path of the pem file, and your used password (if any).
Next, and this one was my biggest issue, make sure your server can resolve the host address of the webservice. Ping it first, and if needed, add it to your host file *facepalm*
Finally, construct your soap envelop (I've used a public PHP WSSE library for mine), and execute the request.
Feel free to ask more details if need be.Go to the full post