You cannot use a PAP2 device that was not made for Vonage as Vonage has their own firmware in the PAP'2's that they sold. If you call to support, they can give you some options for getting another device. Vonage also keeps their ATA's, what even brand they be, user locked.
If this was a PAP2 that was used by you for Vonage, and you don't owe Vonage any money, they should let you set it up for your parents to use.
There's also the possibility of going with some other VoIP provider that lets you "bring your own device", if that's a viable option for your parents. Then you're not stuck with the inconvenience of proprietary hardware etc.
Well Vonage in my opinion is just glorified VoIP... it's in no way or shape better then VoIP.ms.
VoIP.ms is a high quality service... maybe even better then Vonage for a fraction of the price.
I moved my Mom from a Bell line to VoIP.ms ... do you think she even noticed?
Yes she did... she said it sounds so much better and louder & her bill for phone service went from $80 a month to less then $10 and she loves that part best!
I had Rogers Home Phone and it was costing me nearly $50 a month. With voip.ms I'm down to about $4/month (note that I don't talk on the phone all that much). But even if they use the phone a lot, they can probably talk quite a bit before getting into Vonage or Bell territory in terms of prices.
My number was ported from Rogers in 7 days, no problems whatsoever. Whether Vonage play nice with ports, that I don't know (I have read that some companies take their time porting numbers to a new provider).
My mom's port from Bell was a 1 week wait... VoIP.ms sent me many emails to keep me up to date, they even knew the time of day the port would take place.. sure enough it did happen at that time... it was seamless and all went well.
The only weird thing I noticed is that the morning of the port, my phone number wasn't working. I first checked around 9-9:30am. Then around 1pm I checked again and the number was working, and a minute later I had an e-mail from voip.ms saying the port had been completed.