I found some information on this topic by searching around the internet, I have tried this information and it works great for me. Please note that I have not created any of this content, I am just mirroring it.
First things first –
Download: SP2KPAP2.zip
Download: PAP2SP2K.zip
DO NOT CONNECT THE PAP2 TO ANY NETWORK WITH INTERNET ACCESS until directed. The unit will attempt to connect to a Vonage TFTP server on power-up and update firmware without your intervention. If this happens the unit could become a brick. Keep the unit isolated until these parameters are changed and you are directed to connect the unit to the net and/or public internet.
New Unit -
A new “out of the box” pap2 will not have ANY network parameters setup (IP Address, IP mask, gateway, etc). First, configure the pap2 via a touch-tone phone with minimal IP information that will permit later access via your web browser.
Review Chapter 4 of the Linksys pap2 Installation and Troubleshooting Guide.
Connect a standard touch-tone phone to port #1 and make the following changes:
a) Disable DHCP - ‘****’, ‘101#’, ‘0#’, ‘1’ hang-up
b) Set Static IP Address - ‘****’, ‘111#’, ‘192*168*2*10#’, ‘1’ hang-up
c) Set Network Mask - ‘****’, ‘121#’, ‘255*255*255*0#’, ‘1’ hang-up
d) Set Gateway Address - ‘****’, ‘131#’, ‘192*168*2*20#’, ‘1’ hang-up
The following steps have set the pap2 IP address to 192.168.2.10, mask 255.255.255.0 & gateway of 192.168.2.20. This document will utilize these addresses later. If your network uses different address/mask/gateway adjust accordingly.
Reboot the pap2 and use the phone to confirm the changes were saved. You can also check around to determine current firmware version, MAC address, etc. You don’t need them for later steps, but feel free to check them out. NOTE: you will be unable to enter the ADMIN account at this time (unit is locked).
Change your DNS addresses –
Modify the DNS (Primary & Secondary) to match your ISP’s DNS values. It may be necessary to change these at a later date to ones associated with the VoIP provider.
Isolate your network from internet –
For this next sequence disconnect your LAN from access to the public internet. Also, DO NOT ATTEMPT to update firmware via a wireless connection – bad results. Hardwired connects only!
Install tftp server utility –
Included on the CD-ROM is a free tftp server utility – tftp-desktop-free ver 2.5. Suggest you use this utility because you can monitor the firmware download/update process. This can be downloaded from www.download.com, search for tftp. While this utility is free, it’s possible it can only be used for 30 days. You may need to get a “fresh” download.
NOTE: The tftp utility installs nicely under WinXP and creates a directory in /Program Files/TFTP Desktop . You will need to know this in order to copy the firmware images to that area and rename the files.
ALSO: The utility does NOT start/run automatically when your system is booted. It is necessary to click on the ICON to start the utility.
Uncompress/Copy Firmware Image Files –
Two Firmware image files need to be unzipped, renamed and placed in the tftp default directory, which is /Program Files/TFTP Desktop. Uncompress the following files:
pap2SP2K.zip and SP2Kpap2.zip. After the files are uncompress into the tftp default directory it is CRITICAL to RENAME the file to correct a naming error. The files must be renamed to add a ‘-‘ as follows: pap2SP2K.bin to pap2-SP2K.bin and SP2Kpap2.bin to SP2K-pap2.bin
Next, if your PC/Laptop does not have a static IP address you should assign one at this time. While not absolutely necessary to have a static IP address, your IP address must be known (and does not change) in order for the pap2 to find the tftp server and thus the firmware to be downloaded. For purposes of this example the tftp server PC has an IP address of 192.168.2.110, mask 255.255.255.0
Connect the pap2 ethernet port to your isolated network. Remember, you don’t want the pap2 to get to the internet – not yet!
Next, ping the pap2 device to make sure your network connection is working.
PING 192.168.2.10
START OF FIRMWARE UPDATE -
Open a browser and enter the IP address of the pap2:
»192.168.2.10
You should have opened a Linksys pap2 configuration page on the INFO tab. Select the SYSTEM tab. Enter an USER password of 1234 and at the bottom of the page select SAVE SETTINGS.
Now refresh your link and you should be prompted with a login screen.
Enter a User Name of USER , password = 1234
Keep this browser page open, but shift it down to the lower right section of your display.
Next, start the tftp server utility and position the window in the upper left section of your screen. This is to permit monitoring the firmware download process.
Next, return to the open browser page and position the open window such that you can continue to monitor the tftp desktop window – keep at least 1/3 of that window visable.
Update the browser address line and enter the following: »192.168.2.10/upgrade?tftp://192.···SP2K.bin
Monitor the tftp window and you should see a progress bar indicate the download status.
At this time the Power LED should turn RED.
Wait at least 1 or 2 minutes after the status shows complete – do not interrupt it.
Once RED, update the browser address to your pap2. (our IP in this example is 192.168.2.10) login using user account USER , password = 1234
At this point you should now see a Sipura Phone Adapter Configuration screen.
Click the “admin login” link near the top-right.
Click the “advanced” link near the top-right.
Click the PROVISIONING tab and set PROVISION ENABLE=NO.
Click SUBMIT ALL CHANGES.
At this point you might get an “unable to display” page on your open browser page – don’t worry about it – leave it as is.
Next, update the browser address line and enter the following: »192.168.2.10/upgrade?tftp://192.168.2.110/ SP2K-pap2.bin [ver 3.1.3]
Alternate version
»192.168.2.10/upgrade?tftp://192.168.2.110/ pap2-BIN-03-01-06-ls.bin [ver 3.1.6]
* * * * *
Again, monitor the tftp window and you should see a progress bar indicate the download status. Wait at least 1 or 2 minutes after the status shows complete – do not interrupt it.
The Cisco/Linksys pap2 will eventually reboot (2 solid blue LEDs) (BE PATIENT)
DONE - The firmware update/unlock is now complete.
When you login to the pap2 unit you will again have a Linksys pap2 configuration screen and you should be able to access the ADMIN LOGIN link without a password.
The unit is now unlocked and can be configured for various VoIP services. You can now safely connect the pap2 unit to a network exposed to the internet. HOWEVER – never attempt to do a FACTORY RESET – or your unit may be locked again to Vonage and might not be unlockable a second time. Still working on it.