Does the iPhone use Wi-Fi for everything or just for data?

When you have your iPhone connected to your wireless network at home does it use that connection for everything like voice calls, Internet, and text messaging or does it maintain a simultaneous link to the cellular network for things like voice calls and text messaging?

Your phone uses cellular network for calls and text messages, since these don't require a Wi-Fi to work. (Excluding iMessage, which needs an Internet connection since its Internet based.)

Still don't get why people think that internet is required for calls/texts. They never have. Still don't. The iPhone uses Wi-Fi whenever possible over a data connection. When the Wi-Fi drops the 3G/4G takes over.