There are two ways to do this -
1: perform a factory reset while the unit is off the internet, log in to admin, and disable the provisioning options, and change the admin password. This will also work with new units that you have not activated or connected to internet yet.
To do this you will need a hub or cross over cable, and a phone attached to the unit. You also need a PC (or web appliance) in the same subnet as the unit in order to log into the admin once it is reset.
With only the power and phone attached, (no cable to phone on wall socket or network yet) dial "****" followed by "73738#" "1"
Now restart it and Attach the unit to network (but not internet) and let it get an ip address - you can confirm IP by dialling "****" "110#"
Load the IP into a webbrowser of a machine on the same IP network and disable provisioning and assign your own password. At this point save settings and unit is safe to connect to internet.
Optionally if you have firmware and an uploader, upgrade the firmware to prevent it ever being accidentally provisioned once reconnecting to the internet.
* Testing - sucessful on an engin 2.X firmware series SPA3000 *
2: use the very provisioning system they locked it with to begin with to unlock it.
To do this you will need, a hub or cross over cable, a PC running a DNS(eg tinydns or residns), DHCP server (eg vdhcp), and webserver (eg webweaver).
You will also need a "spa.cfg" in either Sipura XML format, Sipura text conf format or SPC.exe (SPA2000 or SPA3000 Sipura Profile Compiler) MAC ID format. (See this other guide for details how to use that)
The format you need varies depending on the model and firmware loaded. SPC format works on all, but it is very hard to source a copy - and requires linking to your SPA Mac address, so there is no point posting a link for one! XML seems to work on some 2* series firmware units, and conf seems to work on some 3* series units.
The pc will need to be configured to the IP of the provisioning server, and the DNS should resolve all IPs to itself. DHCP should assign itself as DNS and gateway. You will likely need subnet of 255.0.0.0 set in DHCP to complete the trick
On engin you should try IP 18.104.22.168 or 22.214.171.124 as the PC IP as their current script connects direct to IP.
If you dont know the provisioning server IP of your provider, install a packet monitor/sniffer like analogX's packet monitor, and use any IP's you like in dhcp to give your pc and SPA IP's. Start the packet mon up and power up the SPA, you should see the IP get assigned, then a number of UDP and eventually TCP requests sent out - the initial UDP requests that link to an ip other than your DHCP/DNS/WEB server ip, eg 126.96.36.199 is likely the IP you need.
Once you have figured out the IP your fake gateway/DNS/webserver needs, power down the SPA, and make the required changes.
On your webserver you need to create a folder in the WWW root folder called "sipura" and another folder below that again in lowercase composed of your SPA units mac address (you can get this from sticker or DHCP lease record) eg 01fe841e101
Grab whichever file you want to try to use from above, (for me the XML file worked) and rename it to lowercase - "spa.cfg" copy this file into the mac address titled folder, and power up your SPA. After a few minutes it should connect to your webserver and grab that file. Give it a few seconds after it grabs it, then power down the unit. Power it up again, and using your web browser, browse to the IP address of the unit, you should get in with no login prompt, go to the provisioning tab under advanced, and set it to "no" or "off" depending on your version. Apply/Save your changes then you can safely reconfigure the unit however you like, and it should still connect to your line 1 primary VOIP provider.. Only now you can set another provider up on line 2!
* Testing - sucessful on an Engin 2.0.10 firmware series SPA2000
Have Fun .. Regards PhoenixX