Hi See here Giffgaff abroad All giffgaff sims are enabled for use abroad. Remember goodybags and gigabags, and free giffgaff to giffgaff are for uk use only. You need credit in your account to use your phone abroad. You need to check that your network carrier is set to automatic in your phone settings. This will allow your phone to connect to O2's partner networks all over the world. I would also disable data roaming, and use wifi where possible, as data usage abroad is very expensive, and disable voicemail ( Dial 1626 ) You can also enable auto top up on your gg dashboard. If your balance drops below £3, you can set it to top up your credit by a set amount, this has to be done by entering a debit or credit card number.
See link below for a detailed guide for using giffgaff abroad.