Nope, it's definitely a prepaid offer as well:
http://www.abroad.vodafone.co.uk/index.cfm...me=a2&nu=1&le=2
"With Vodafone Passport you can use your mobile abroad as often as you like. Whether you're a pay monthly or pay as you talk customer* you just pay a 75p connection fee each time you make a call and, after that, you?re charged at your usual home tariff."
"*Vodafone Passport is currently available on Perfect Fit price plans available as at May 1st 2005, 3G price plans, Smartplus and Smartstep."
(The last 2 plans are prepaid Pay As You Talk plans).