I'm heading off to the UK soon and will be taking my phone with me. I use Vodafone and the plan I use is My Flex Prepay. I'll be away for one month.
In the past when I've visited the UK I've always popped into a Vodafone store and they've given me a UK SIM card and I've bought one of their pre-pay plans (eg a £10 Bundle gets me 7GB data, unlimited calls and texts) and this has been more than enough for my uses. When I get home I replace the UK SIM card with my NZ one and throw away the UK card. I find that this works out cheaper than using the Vodafone NZ pre-pay roaming ($6/day or $22/week). I won't be calling or texting anyone back in NZ while I'm away, I'll use a messaging app if I need to get in touch with anyone.
This time I'll be traveling with a duel SIM phone for the first time and I was considering leaving my NZ SIM card in the phone and adding the UK SIM card and telling my phone to default to the UK SIM card for data/calls/texts.
What happens if someone calls or texts my NZ number while I'm away? Do I have to pay to receive the call/text? The only info I could find on the Vodafone site says that the caller doesn't pay anything extra.