I found this, not sure if it would work for you though?
When I was a Sky subscriber, Sky accepted my VoIP number, it's an 0121 number, so no matter where in the world I am I have a UK - Birmingham number, it just looks like a usual number.
I have my VoIP line set up at home (don't have a landline) and I can have my VoIP set-up in another country at the same time, so if I am in Germany for example and I have se up my VoIP when someone rings my 0121 number it rings my phones in the UK and the phones in Germany, if I make out going calls whilst in Germany it sends my UK-Birmingham 0121 number as CLID.
BTW this isn't me!