Samsung Galaxy S II :: Block All Incoming Voice Calls But Not Block Incoming Texts?

I have a S2 on UK Vodafone contract even though I am currently living in NZ. My phone is a UK model.UK Vodafone have terminated the Passport service as of 1st November which means I now go on to NZ roaming which at �1.65/NZ$3.30 a minute is somewhat steep - I also pay that amount for the incoming call.I now need to block all incoming calls on my phone so as I am not tempted to answer calls at odd times of the day or night (quite hard when we are 13 hours ahead of UK and totally out of sync with them) and pay extortionate amounts of money BUT I need to leave the phone available to make and receive text messages.It is not as easy as to just get a NZ phone contract as this was my life line with friends and family in UK until my provider pulled the passport service so need to disable the phone I have.how to do this so as I can still send/receive text but NOT receive voice calls on my S2?