Public Mobile SIM cards have "3-in-1" or "multi-fit" perforations which allow them to be broken down into all three standard SIM card sizes.
You can easily make them smaller. That's how they were designed.
But you can't easily make them bigger. They usually won't work after they've been separated, even if you put them back together again (you can buy adapters which allow smaller SIM card form factors to fit into larger SIM card slots, although these tend to be somewhat unreliable and they typically cost more than a new PM SIM card anyhow).
Your PM SIM card is linked to your PM account and your phone number - and you can't have more than one active SIM card simultaneously linked to the account and phone number, if you activate a new one then your old one becomes deactivated.
But, aside from these form-factor differences, you can freely transfer your PM SIM cards between any compatible devices. You will of course need to configure your Samsung operator/APN software settings for Public Mobile (and restart it), it will then automatically use your existing PM account and phone number. You can then freely transfer the same PM SIM card into any other unlocked Telus-compatible phone (with a compatible SIM card slot) if you wish.
You should be certain that your Samsung phone is compatible with the PM/Telus network and that it is not carrier-locked before cutting down your PM SIM card - it's a one-way move which would suck if your new phone doesn't work on PM while your old phone doesn't accept a (now) smaller SIM card.
