I bought a Wind sim for my iphone 5 at Termini. They told me it would take 2 hours for it tone activated. I had all sort of troubles getting it to work though. I had to change the APN, and my iphone get insisted I needed to deactivate it. My problems were this:
When I landed I had turned cellular data off
Inserting the wind sim in my iphone asked to unlock the sim and for activation (is this a new ios 7 feature?)
With data off I was unable to activate the iphone.

Solution: before removing your old sim make sure your cellular data is on, remove old sim, insert new sim but do not unlock it yet. Go to settings and change APN. Then unlock the sim and proceed with activation. It took me a couple hours to figure that out.

FDW
Cellular data was off