The Sipura 2100 is primarily a first-class SIP ATA, with just enough routing features to satisfy folks whose Internet access needs are simple. Its target user is someone who has only one computer tied to a broadband connection and wants to add VoIP service without too much muss or fuss or losing their computer's Internet connection.
After my time with the 2100, I have a better appreciation for why most VOIP service providers prevent their customers from futzing with the settings on the VOIP hardware they provide. While SIP is simple in concept, its flexibility and extensibility can result in so many bits to play with, that the average consumer networker would be bound to mess something up.
However, I'm still in the camp that says if you buy something - as you do when you purchase retail VoIP hardware - it shouldn't become a doorstop if you choose to change service providers. That unfortunately isn't the case with Linksys' co-branded VoIP hardware that you can buy from your favorite retailer. But at least until Linksys decides otherwise, Sipura ATAs provide the freedom of choice that experienced VoIP users demand.