To get a SIP trace from ADSL, is a little tricky but if you manage it here are the steps which may help,
1. Setup an OpenSIPS server as stateless proxy.
2. In ADSL set that server as Outbound Proxy.
3. Make a call, it will pass through OpenSIPS where you can do a SIP trace.
4. You can even modify SIP requests and replies there and get a hint of their restrictions. For example change user-agent in INVITE from ADSL to FS's user-agent, and see what happens? Does the INVITE gets rejected? etc. etc.
Some security paranoid providers even do restriction based on your ADSL device's MAC address, which is issued and activated by them. Still there are ways to get into their network. All that matters is how badly you need that provider. ;-)
Thank you.