I know Monaco is not currently part of the EU roaming countries but I was wondering if it could be added? I went to Monaco Telecom (the only service provider in Monaco) and asked about this. They said they would contact giffgaff and inquire about adding the principality to your list of roaming countries. I think it would be a great addition, and perhaps easier to do than usual since Monaco is such a small country. I have tried connecting to french networks from within Monaco to have access to my plan but it doesn't work, the connection is either too poor or simply fails.
Let me know if this is something that might interest you. Would love for this to happen!