If today is your transfer day, read on:
What to expect on the day your number transfers:
Number transfers are done in batches throughout the day from about 9am until 9pm. There's no way of knowing in advance what time yours will start or how long it will take.
Whilst the transfer takes place all credit and goodybags will be removed from your account. These will return when the transfer is completed. Do not attempt to add more credit / another goodybag during this time, as you risk losing the money.
You will lose service on both SIM cards (could be at different times). After you lose service on your giffgaff SIM, turn your phone off for 30 minutes. Thereafter restart it every 30 minutes until you get service back. Please be aware that this may be just a few minutes or several hours later
Even when your number appears to have transferred to giffgaff (and you may receive a text saying the transfer is complete), there will be lots of things going on in the background, so expect the unexpected and be prepared for erratic service for the rest of the day. You only need to be concerned if your giffgaff SIM is not fully working with your ported number after 9am the following morning.