To sign up with Vonage you just need to go to their web site

Register online and they will send you an adapter to plug into our router.

Once the adapter has turned up, log into your account on the Vonage web site to arrange for your landline number to be transferred.  They will look after everything and once the number is transferred your old account should be cancelled automatically. 

Once you have been with Vonage for three months they will send us £90 to pass on to you.