How to activate a micro sim?

I got an iPhone 4 and i put my vodafone sim in, its been 24 hours and still hasn't activated?

Have you called Vodafone? You need your network to activate your SIM and then connect the phone to iTunes (or connect over Wi-FI) to activate the phone with Apple.

Vodafone Pay Monthly Customer Services
Dial 191 (free) from your phone or 08700 700191 from another phone

Vodafone Pay as you go Customer Services
Dial 191 (25p per call) from your phone or 08700 776655 from another phone