At home, my iphone has a strong signal to Verizon's 3G network and my home WiFi network. In the interest of battery life, which connection will iphone use if it has access to both networks? Also, given strong connections to both networks, what's the best way to optimize for battery life?
iPhones will always use a wireless connection if one is available (and it is authorised to use it). It will then use 3G (EV-DO). And then 1xRTT as a last resort. So it always prioritises wireless if available.
Wireless is generally better on battery life too.