I used to use VOIP and yes it worked very well, including the call divert.
It initially cost about £15 but came with a £10 credit voucher, which I used and initially also purchased more credit, but then eventually the company stopped recognising me and because I didn't use it very much gave up on it.
Actually I think the company closed down, but not sure of that, or it may have been because I stopped using it for a long time, don't know.....
I gave up on it mainly because I bought it just for the USB handset but didn't realise that credits had to be bought to be able to use it.