The wifi option on my iPhone 3GS is greyed out, what do I do?

I need an answer quickly as tomorrow I am travelling and I put my phone in the washing machine by mistake, I needed a replacement phone quickly so I only had a iPhone 3GS as a spare phone. I set it up and wiped it's Setting and Contents, when I did I attempted to turn on my wifi but it is greyed out. What do I do?