iphone 4 and home wifi issues

Router? iOS version on your phone? Encryption used on your network? More details are always better.
The following are a series of general WiFi troubleshooting steps:
1. Reboot your router - simply unplug the power cord for 30 seconds
2. Reset the iPhone network settings - tap Settings > General > Reset > Reset Network Settings
3. When the phone restarts, tap Settings > WiFi > Other and re-enter your network name, security, and network password.
On the router side of things, do not use WEP. Besides being very poor from a security standpoint, the iPhone/iPod touch dont play too well with it. Change it to WPA2 and use a good 8-12 character password. If your router is more than a few months old, check the makers website for a firmware upgrade. Download and install it.
Let us know if you still have problems.
iMAC 20", iMAC 21.5" Mac OS X (10.6.7) iPhone4 iOS 4.2.6, 2G touch iOS 4.2

This happened, to me and we found out that our internet provider didnt let me join because my brother downloaded music illegally. They said that it was because they didnt want to be involved with copyright infringement. Happened to me yesterday, unsolved.
Samsung Windows 7