If you have up your SIM in a Vodafone store, it'll already be activated for you. You can just insert it into the mobile phone and start using it.
If you ordered a free SIM online, you'll need to call 17298
free from your Vodafone mobile to activate it.
Before activating (registering) a Vodafone SIM card, make sure that the mobile phone is locked to Vodafone network or free from network restriction. If it is locked to any other network, you need to unlock it in prior. You can unlock a mobile phone safer and easier using unlock code. If your mobile phone is a Blackberry model, You can visit UnBBLock.Com
to get the unlock code. If your mobile phone is from any other model, visit Mobile-Unlocker.com
to get the unlock code. Good luck.