How do I know if my phone is blacklisted?
Unfortunately some phones display messages such as "SIM not accepted" if they have been blacklisted making it really hard to tell the difference between locked and blacklisted handsets. Others just don't switch on or behave in other ways which is dependent on the make/model of handset.
You can check if a particular phone is blacklisted by visiting Checkmend - there, for a fee, you can enter the IMEI number of the phone (usually found under the battery compartment) and receive a report that will tell you if the phone is stolen or not. The Checkmend service is independent of giffgaff and giffgaff does not receive any share of the fees paid to them.