Can I use my UK mobile phone?

You need a UK billing address ...to have a UK phone / sim card....you should get ßaway with using your UK mobile and UK sim in Spain for 6 months and then you will be cut off....if your UK mobile is open to all networks buy a Spanish sim card pop it into your Mobile and it should work OK .

Hi Sharon

me and my partner been here 9 months.  both on different networks.  we use wi fi where possible to search internet, send emails etc and use WhatsApp or FB to message or call anyone.  I have 5mb limit each month but because I log into the wi fi where ever i go I rarely use 2gb.  I have not had any warnings from my provider neither has my partner.  we do have .uk bling addresses.  I think I have sent a max 50 texts in 9 months.  I have called .uk and Spanish numbers without fb or whatsapp.  obviously calling Spanish numbers costs if u do not use FB or WhatsApp.  also calls to .uk mobiles come out of my unlimited calls so r free.  again never had a problem in 9 months.

Can you just put a Spanish sim in the existing phone?

I'm with EE  with a UK number unlimited texts unlimited calls national /International calls. 4G. And they're quite aware I live in Spain 

I can put a Spanish SIM in my phone but don't need to as I can use as .uk phone.  most of my friends who have Spanish numbers have WhatsApp.  it's only utility companies that e my prob 

Me too 😊

I wonder if you get charge ...at international rates if you use your EE UK reg mobile if you call a Spanish number when in Spain ...I am on UK 3 network it does not cost me anything to call the UK but if I call a Spanish number I get charged as if I am making a international call .so if that's the case I cannot see the advantage of using a UK registered mobile/sim if you are a Spanish resident .

If you have a smart phone and have had it for more than a year, you can almost certainly get it unlocked legally.
I did it with my two Samsung phones which are with O2. They provided a key and instructions. There was a fee. Howevere, it's probably safer than taking your phone to a back street hacker.

I can now use any SIM (I have a Spanish one) and an EE Pay as you go. Both work perfectly.

If back in the UK, you can put your original SIM back in the phone and it will work. Provided your contract is still running.

You should check with your provider as to how long you are permitted to continually use your phone while abroad. It's usually 3 months, but that gets reset each time you return to the UK. 

Het a Hits Sim ...either PA.yG or monthly contract....very cheap, theres wifi to log onto everywhere so you don't need to use your data all the time. If your phone is unlocked just change the Sim card.