If anyone wants to try I have successfully registered VOIspeed SIP trunks with Cluana. Most settings are really straightforward but I reported them below if you wish to have a go:
Step 1) Create a new line for the VoIP account in question: Settings –> Lines –> Add a new phone line.
Step 2) Enter the description of the phone line (e.g. VOIspeed VoIP line) and the phone number or the account number.
Step 3) Select VoIP from the drop-down menu.
Step 4) Enter all settings as follows:
Username and Password are given to you when you create the new VoIP account
Realm = Proxy = Domain = sip.xxxxxxx.com (which is also given to you when you create the VoIP account)
If you have done everything correctly the new VoIP account should register straight away (check the status going to Monitoring Lines and you should see a green light on the Sip trunks in question).