My iPhone refused to connect to my home wireless network. It is set up to use WPA, and my Mac OS X iBook, a Windows XP laptop and even my old Windows Mobile phone could all join the network happily. Not so my shiny new iPhone. It complained. I eventually tracked this down to my WPA password either being too long (18 characters), or that it had a non-alphanumeric character in it (single quote). I changed it to a 9-letter password (all alphabetic characters), and all is well.