Permanent divert on no reply

[#1]

This might be a bit of an obscure one but I'll ask it anyway as I think this is the best place to find an answer.
I'm in the process of moving to Plusnet for my landline having previously had a Sipgate VOIP "landline" via my Virgin cable broadband (which I have also abandoned as it was £23 per month for broadband only!!!)
The thing is, the Sipgate voicemail is great with a lot of good features and I'd like to retain it. Someone on the UK.telecom newsgroup suggested I could ask Plusnet to set up a permanent divert on no reply to my Sipgate voicemail number. I'm not talking about wanting to set up (and pay for!!) call divert with Plusnet but more a one-off permanent arrangment of diversion on no reply. The person who suggested this also suggested that Plusnet might do this for a one-off fee.
So Plusnet, can this be done, what do I ask for and how much would it cost?
Thanks

[#2]

Hi there,
We can certainly arrange a permanent call divert to any given number, though I'm afraid to do so costs £2.50 a month - I'm not sure if we could do it for a one off fee as we're charged monthly for the same thing, to my knowledge there isn't a way around that though I will ask for you.