If it's just a new SIM for the same account it should be the same out of the box. If you transfer to a new provider you can transfer the number, just get a
PAC/MAC code, or whatever the Greek/Botswanan equivalent is, from your current provider.
I transferred from O2 to T-Mobile for the 4G network rollout and took my number with me. Normally takes 24 hours but, due to the numbers doing the same, it took 48 hours.