See my post in message 5.
Just plug a third party ATA into the hub.
(I currently have an 033 number with A&A, £1.56 a month PAYG).
Then I'd suggest buying an ATA from them, as they will preconfigure it and it's a surprising complicated little beast by today's standards.
There are only a couple of changes I would recommend
1) Changing the passwords, including the SIP password, (as theirs is based on this four random words nonsense). Note it needs to be changed on their website and the ATA.
2) Reset the time zone. The latter is only really important if your phones display the time. For some reason the time zone is set to use "self defined time" which doesn't work. Putting on GMT, London works fine.
Reading their help files on the website is also highly recommended as there are one or two other things worth doing.