Your router uses a technology called Dynamic Host Configuration Protocol to assign a unique IP address to each device on your network. If your iPhone is connected to your wireless hot spot, but you're unable to access websites or other Internet services, your phone may be sharing its IP address with another device on the network. To obtain a new IP address from your router, refresh your network configuration from the Settings app. Your iPhone will release its existing IP and request a new address from your router.
Tap "Settings" from the Home screen and then touch "Wi-Fi."
Select your wireless network and then scroll to the bottom of the screen.
Touch "Renew Lease" twice to reset your IP address.
You can also set up your iPhone to use a static IP address from the Wi-Fi screen in Settings. Select your wireless network, touch the "Static" tab and then enter your information into the "IP Address," "Subnet Mask," "Router" and "DNS" fields. Contact your Internet service provider if you don't know your network details.