Hey everyone! I see a lot of posts in the community asking whether an O2 locked phone will work with a giffgaff SIM card, I also see many asking if a giffgaff SIM card will work with phones locked to other MVNOs of O2 such as Tesco Mobile... So in this single post I will answer both of those questions for anyone who needs them answering, I also intend to say why it's like it is!
To clarify, giffgaff SIM cards will work wilth all phones that are locked to O2-UK... (As will other O2 based network SIMs). GIffgaff SIM cards will NOT work in phones locked to Tesco Mobile and other MVNOs, just like O2 SIM cards won't work in Tesco Mobile locked phones.
So why is that the case?
Firstly, a phone can be locked to either a base network or to a specific network...
If a phone is locked to a specific network (Tesco Mobile for example), then a SIM card from another network (Like giffgaff or even O2) will NOT work, even if it still uses the same base network (O2, in the case of Tesco)... This is because more often than not, Tesco (or other networks) double lock the phones, so it will be locked to O2 as the base network then locked again on top of that to the specific network (Tesco).
Some people have reported they have got phones from Tesco on Tesco Mobile and they have worked with a giffgaff SIM, If that happens it means they have not bothered to double lock it, it does NOT mean some double locked phones work... However they do double lock 90% of the time so DO NOT take any chances if you are not prepared to get it unlocked!
Hope this has helps you all understand it better!
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