I moved my FTTP broadband to Plusnet Full Fibre (with Smart Hub 2) and my home phone service to Vonage last month, after a very unsatisfactory experience with BT Digital Voice. Setup was a breeze, and all is working well so far.
The only minor niggle is that I am not getting an intermittent dial tone to indicate a new voicemail message (perhaps because of handset incompatibility), but that's not a huge problem for me, as I have an answering machine anyway. Vonage also allows you to set up text and email notifications of new voicemail, including the option of having an audio file forwarded to your email. This and other options, such as call forwarding to a mobile if your internet connection is down, are easily configured via the Vonage online interface.
I did not, however, attempt to port my previous BT landline number to Vonage, having read online of the difficulties experienced by others with number porting to VOIP providers. After eventually persuading BT to prematurely end my contract without penalty over their Digital Voice failure, I just wasn't up for another battle to keep the number and instead chose a new one during the Vonage signup process (you can keep refreshing the numbers offered until something memorable comes up!).
I previously used Vonage over an FTTC connection when I lived in Canada and never had a single problem in 6+ years.
