1. goto settings (the spanner icon) then scroll to the end and select "about product" from the "general" list. If the penultimate number of the Version is .203. then you have the "unbranded" UK generic version, so any SIM will be OK; if it is .205. then you have the Vodafone supplied version. But even if it is Voda supplied, I believe it is still provided unlocked (can anyone confirm?) - if so, any SIM should still work regardless. There ws a problem with some older "3" SIMS but that was fixed in a recent firmware update.

2. see http://shop.vodafone.co.uk/pay-as-you-go/hub/vodafone/ : "Calls cost 20p a minute and texts are 10p - to anyone, any time, anywhere in the UK."

3. this just means the SIM will work in any unlocked phone. If you do get a SIM make sure you get a 3G one if you ever intend to use data.

EDIT - ok, just saw link in your second post - sounds like my advice in (3) was wrong then .. appears to be a special SIM just to unlock a phone that's currently locked to Voda. but you shouldn't need it anyway.

EDIT#2 - did a bit of googling, turns out this is used in addition to a SIM (from another operator) so that you can use that SIM in a handset that is locked to Voda. So the handset remains locked & you don't invalidate warranties etc. You live and learn :-)