My iPhone 4 keeps saying, "can't scan for wireless network" and I've just installed a new home wireless network! Why won't my iPhone recognize this new wi-fi or scan for any network now?
migrated from superuser.com May 2 '11 at 1:24
Try resetting your Network Settings, in the settings app, under General > Reset > Reset Network Settings.
Failing that, backup your iPhone to iTunes, and Reset the iPhone to new, then try and connect to the Wifi network, if it does connect, restore your iPhone from the backup, and it should be able to connect.
The last option is to take it to an Apple Shop (even if you're past warranty)
The first thing that comes to mind is the fact that the iPhone 4 only supports 802.11n on 2.4GHz. So if the router is using 802.11n on 5 GHz, the phone won't be able to connect. Check the router's settings to see if you can change that.