WIFI not being detected on iPhone 3G

I am trying to use my old iPhone 3G as an iPod touch for my child. When I was using it as a phone and had service with AT&T I had no issues connecting to our WIFI but am unable to now. The WIFI does work on my daughter's iPod, my new iPhone, and my pc. I have gone through and reset the settings, ensured WIFI is set to on, etc but it won't even detect the WIFI available.

Is it because I no longer have a phone connection or did it just happen to break immediately after getting a new phone? What can I do to fix it?

Help please.