Yes, I had problems believing it too, but they have taken fairly strong exception to Vonage ads following a complaint from BT. Full judgement is here (http://www.asa.org.uk/asa/adjudications/non_broadcast/Adjudication+Details.htm?Adjudication_id=42801).
What particularly interested me was that the ASA rapped Vonage for an 'unlimited' claim. Seems a very different stance to that they take over broadband ads. :(