Hi @Matthew Brookes, welcome to the community!
If you’re looking at changing your existing 24-month plan to a SIM only, you’ll be able to do so by upgrading via the iD app or your account online. You wouldn’t need to opt for a new number necessarily. The upgrade deals will also be visible on your account for a Google Pixel. However, it’s likely that the giftcard will only be available for new customers.
However, if you have upgraded to a SIM only plan already, you would only be able to upgrade that plan again in 6-months time.
If you’d like to discuss your options further, it’s always worth calling our sales team to see what they can offer. Their number is 0207 1391 397. Alternatively, if you have any further questions, feel free to ask here!
-Lauren