My Iphone wifi button is grey out

Resolution First, sync your iPhone or iPod touch to iTunes to backup your user information, Contacts, Calendar, and other data. Then try the following steps in order.
One On the device, tap Settings > General > Reset > Reset Network Settings. Check to see if the device now displays the Wi-Fi address or Bluetooth address (tap Settings > General > About and scroll down to Wi-Fi Address or Bluetooth). If there is a Wi-Fi address and a Bluetooh address, then you're done with these steps and you can resync your settings and your media using iTunes.
If there's still no Wi-Fi address or Bluetooth address, then continue to step two.
Two On the device, tap Settings > General > Reset > Erase All Content and Settings. Check to see if the device now displays the Wi-Fi address and Bluetooth address (tap Settings > General > About and scroll down to Wi-Fi Address or Bluetooth). If there is a Wi-Fi address and Bluetooth address, then you're done with these steps and can resync your settings and your media using iTunes.
If there's still no Wi-Fi dddress or Bluetooth address, then continue to step three.
Three

1. Restore the iPhone or iPod touch software (this erases all data on the device) using iTunes (see article 305744 for additional assistance).
2. After the restore is complete, sync your previous settings (mail settings, text messages, notes, call history, contact favorites, and so on).
3. Now see if your device shows a Wi-Fi address and Bluetooth address (tap Settings > General > About and scroll down to Wi-Fi Address or Bluetooth).

If there is a Wi-Fi address and Bluetooth address, then you're done with these steps. If there is no Wi-Fi address or Bluetooth address, then continue to step four.
Four If there is no Wi-Fi address or Bluetooth address listed after doing the above steps, then your iPhone or iPod touch may need to be repaired. See the iPhone Service FAQ or iPod Service FAQ for additional service information.