21-05-2020 06:40 - edited 21-05-2020 06:45
Yes, perfectly possible - so long as your phone's Sim format matches - micro Sim vs nano SIM, for example, @Shedden. Also an older 4G Sim may need to be changed if your new phone is 5G capable, for example.
on 21-05-2020 07:15
Can you clarify your question please as I read it differently to @pgn
If you take a refresh contract you must take a new airtime tariff too. So whilst you can use your current SIM, it will have a different tariff attached to it.
OnePlus 6 (O2 & Sfr), Z3 Tablet (Three UK), iPhone 8+ (EE)
on 21-05-2020 11:56
The short answer is no
You must take a tariff if you want a new phone unless you buy the phone outright
In that case there are much cheaper ways of buying rather than through O2.