Vonage and Linksys PAP2 - Can be used for other VOIP?

I am thinking about getting Vonage, and getting the Linksys PAP2 Phone Adapter for Vonage Internet Phone Service.

Question: If I buy this independently - if Vonage dosen't work out, can I use it for another VOIP service, or the PAP2 can only be used with Vonage?

Buy a non-Vonage (unlocked) phone adaptor, and update it's firmware before getting the service you intend to use it with, thus ensuring best use.