I will be out when my new SIM arrives tomorrow but its my switch day so will my current Three SIM stop working? Or does the switch happen when i insert new SIM please. Thanks

​@Juliep1003 Number porting usually happens on the scheduled working day (Monday-Friday), generally taking place between 8:00 AM and 10:00 PM, though many operators complete the switch by 6:00 PM. Service disruption often occurs during this time, with the final transfer taking around 15 minutes to complete. Your existing SIM will show no service at some point during this time. Then you need to put the new iD SIM card in your phone and start using that. 

Hi ​@Juliep1003,

Thank you for your message.

Kindly note that once the switch has been completed, your current SIM will stop working and you will need to use your iD SIM instead.

Please be assured that the switch happens automatically, so you do not need to insert the SIM for it to take effect.

Thanks.

I will have my phone with me when the new SIM arrives so cant swap them over. Will my phone die? I need my phone active until I physically swap the SIMs

As stated above you phone will eventually have no mobile service on your old network. Should be able to use WiFi though as normal until you are able to put the new iD SIM in the phone. This is standard practice when porting a number across for all networks.