if you have ordered a phone from here it will probably come with a sim
do a sim swap you wont lose anything
SIM Swap is the operation of replacing your existing SIM with a new SIM card.
this has to be done between 4.30.am to 9.30.pm
You will be redirected to "My giffgaff" where the "Activation in progress..." message is displayed.
Your old SIM will be deactivated, and you will lose signal. Put the new SIM in your phone, and it takes around 30 minutes for the SIM to become active. When the new SIM is active, you can refresh your "My giffgaff" page, it will display your current balance and / or goodybags again.
The best thing is to leave the phone turned off with the new SIM in for 10 minutes, then turn it on and off until you get signal.