My iPhone 4 won't connect up to the Wi-Fi?

For some reason I'm having difficulties to connect up to my host parents Wi-Fi. My laptop has no problem connecting and works perfectly. My phone on the other hand will never connect, and even when I type in the right password, several times it will say: "unable to connect" I've had to use a lot of 3G just to be able to call my family back home since I'm on student exchange, and this is very expensive! I've also re-rest all of the Wi-Fi settings and forgotten the Wi-Fi network, but, nothing is working and I don't understand why.

Could someone please help me, As soon as possible, I'm desperate!

Added (1). I have also tried to click on "other" under the Wi-Fi settings to manually do it, but, still my phone tells me that there's no network to connect too

3. Avoid IP Address Conflicts
If your computer and another on the network both have the same IP address, the conflict between them will prevent either from working properly online.

Action - To resolve an IP conflict, follow these instructions to release and renew your IP address. If your network uses static IP addresses, manually change your IP to a different number.

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4. Check for Computer Firewall Malfunctions
Firewall software running on most computers is intended to prevent unwanted network traffic from disrupting its operation. Unfortunately, these software firewalls can malfunction and start blocking valid Internet traffic. When two software firewalls, such as Windows Firewall plus a third-party product, are installed on the same computer, contention between the two can also incorrectly block traffic.

Action - If you've recently installed or upgraded software firewalls on your computer, temporarily disable them to determine whether it may be the cause of Internet connection problems.

5. Are You Outside of Wireless Signal Range?
The performance of Wi-Fi network connections depends on distance between the device and the wireless access point. The further away a Wi-Fi device, the slower the local connection generally runs, until it breaks altogether. Wireless signal interference in the area can also limit the effective range of a Wi-Fi connection. Whenever you're unable to reach the access point, you also can't connect to the Internet, obviously.

Action - Use one of these options to measure the strength of your wireless signal and try these ideas to expand the range of your Wi-Fi.

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6. Has Your Wireless Network Configuration Changed?
Wi-Fi networks with encryption options like WPA or WEP turned on require computers to use matching security keys when connecting. If someone changes the encryption keys or passphrase on the access point, devices that worked before will suddenly be unable to establish sessions and Internet connections. Likewise (though less likely), if the access point settings are changed to require using a specific Wi-Fi channel number, some computers may be unable to discover it.

Action - Confirm the Wi-Fi channel number and encryption keys on your router have not recently changed (check with the network administrator if necessary). When using a hotspot, follow the provider's instructors for signing on carefully.

It would be very easy, you can just turn your laptop into hotspot with My Wi-Fi Router software.It's free and you can create a stabale hotspot with encryption very easily, then your phone can keep connected.