2g 3g switch off

[Squidley]

I use a PAYG SIM have done for 18 years. I only top upfew times a year. I don't live in a good reception area but need the phone and WhatsApp has been a lifeline.

. My question is  If I buy a new 5G phone can I just put my old SIM into this phone and carry on topping up as and when needed and not have to have a monthly contract. Thx

[MI5]

@Squidley 

You can use 4g for data, but not for calls.

We don't know yet what will happen for PAYG customers when O2 turn off the 3g network.

They will either have to move everyone to giffgaff or provide the 4g calling option to O2 PAYG sim cards.

[pgn]

To clarify, @Squidley 

PAYG on O2 has no access to

1. 4G Calling, also called VoLTE (tied to WiFi Calling) 

https://www.o2.co.uk/connectivity/wifi-and-4g-calling

2. 5G anything

Not all networks are as restrictive - as mentioned above: giffgaff, which uses the O2 network as its carrier, does support "4G calling / VoLTE" on its PAYG service.