Thanks. I actually called Virgin Customer Service in the UK this morning. The man there assured me setting up the voice mail was a free call, even from the US. Well, of course it wasn't and I'm down to ?1.90 airtime
Next I find out if you want to top up with a credit card, it has to be a UK credit card
The ?1.90 should be plenty for my dad -- he can retrieve any voicemails I leave him for free
Live and learn