Here is the video guide:

I bought them from Amazon for around £3.50-4.

I felt that having the SIM cutter was better than going in-store to ask for it cut each time I needed a SIM to be changed.
Overall, I’m very much satisfied with my purchase, and more so, it work perfectly with the adapter on my Samsung Galaxy S i9000 – which unlike the SGS3 i9300 which accepts micro SIM only, the i9000’s SIM slot is a normal sized one.

I hope the video guide helped you!
–TotallydubbedHD