Yes it is easy to setup. You just put in the proxy, userid and password for the account.
You would be using it a different way, just to access the pstn line without ringing a phone attached to the SPA3102. There are a couple of different ways to do that but they aren't the standard configuration. Put up a thread in the Linksys/Sipura group on this forum when you get the SPA3102.
They don't send you any documentation that amounts to much along with the SPA3012, nor do they make it easy to find any. Grab the ATA Admin Manual that you hopefully can find a link for on this
page. The manual applies to a range of products.
The problem that you can have is the router that you attach ata. No doubt the one in the UK is a different brand from the one at the distant location. Different brands can work differently and can cause different problems. The problems can be overcome, but they are sometimes frustrating.