After learning that the Linksys RT32P2 I purchased was locked to Vonage, I returned it. While at Staples I noticed the Linksys PAP2. I asked a sales person about whether or not it was similarly locked. We noted that it did not list Vonage service under the minimum requirements and he encouraged me to just get it and return it if it didn't work.
Well...I've been trying it. It does indeed appear to be an SPA-2000 under the hood. When it boots, it makes a TFTP request to ls.tftp.vonage.net for "/spa000F66A84007.xml". The Web interface is Linksys-branded but similar to the Sipura devices.
One of the options is "Admin Login". When I tried this, I was unable to authenticate successfully. I called Linksys support in India. After a couple of people told me that there was no Web interface, I made a tunnel to the PAP2 and gave one of the technicians the URL. He tried it. Long silence.
Finally he said that he had examined the URL and determined it to be a PAP2 simulator. Arrghh! It took a few more minutes to convince him that it's the non-existant Web interface on*my* PAP2 that he was seeing. (BTW, another technician told me to hit a reset button on the unit. There is none. She was sure it was "near the lights.")
I finally got to talk to Senior Technician Gordon (in the US?). He quickly explained that it's locked to Vonage. It only took an hour on the phone to get the answer but it was at least a bit entertaining.
BTW, it does appear that the unit can directly dial IP addresses without registering with Vonage. So you *could* use it on its own (especially on a phone with speed dial) or with Asterisk. It's not worth it to me though.
Back goes another piece of Linksys hardware... I'll spend the extra $20 for hardware I control.