@DonutANZ - if you go dual SIM and for example keep your NZ 2 Degrees account still going, I'm guessing you would have to pay roaming fees for the NZ account? I wish I was more "tech informed".
No, it is only if I initiate (send) a SMS txt or make a call using my ANZ SIM that there is a cost.
There is no need for me to do that because my Vodafone Spain SIM allows me to do both those things without a cost.
Data is different.
Without going too deep into the technicalities of it, you can only have a single data source at a time and so it is necessary to choose which SIM you will use for data.
Of course, I always use my phone settings to only choose my Vodafone Spain SIM because that is without further costs.
Depending on your type of phone (Android vs Apple) it is relatively simple to set up the settings so that your Kiwi provided SIM is passively listening for incoming phone calls and incoming txt messages but, by default, won't be used for outgoing calls.
Just be careful with txt replies. By default they will use the same SIM card that they came in on and so I need to remind myself to actively choose which SIM card to reply on or, if I can, I switch the conversation to WhatsApp or Signal because they both use data rather than the SMS protocol.
Also be careful with answering incoming phone calls on your Kiwi SIM. Depending on your local provider if you accept an incoming phone call you may be charged international call rates.
What I do is:
1 educate my friends and family not to call me when I am on Camino unless it is an emergency and then to use WhatsApp or Signal data calls if at all possible.
2 Change my missed call message to reflect that I am currently travelling internationally and asking the caller to email me or txt me instead.
3 Train myself to look at which SIM is accepting the call when it comes in (if you look at your screen at the time then it is obvious) and not to accept calls on my Kiwi SIM unless it is from a close family member (see 1 above).
4 Set my phone to Do Not Disturb each night (also polite for other pilgrims in shared accommodation) so that Kiwi calls and txts don't disturb my sleep.
I have the skills and knowledge to do these things using my phone settings. If for some reason you don't or are unsure then I have found that if you purchase your Spanish SIM card from a major network provider in Spain (such as Vodafone Spain but there are also two alternatives who are probably just as good) from one of their branded stores then the person selling the SIM is often willing to help you with setting up your phone to achieve the above.
Edit: I think that you need to turn on "Roaming" within the Kiwi app/ phone account as well as allowing roaming within your phone settings for this to work.
