You’ll be delighted to learn about a simple hack that lets you run purchased iPad apps on your iPhone 4. Unlike past, a new method for less tech-savvy users is as simple as downloading the iTelePad2Pod app and running the program from the Applications folder on your Mac. Your iOS device must be jailbroken and have OpenSSH installed from Cydia because the tool basically sends the iOS app file via secure FTP protocol to your iPhone or iPod touch. The trick is in changing the app's underlying metadata to add both devices as designated platforms. Some apps won't work due to multitouch and design issues, like refusing to work in landscape.
Others may be tough to operate due to a greater number of iPad pixels compared to the Retina Display on your iPhone 4 or iPod touch, meaning parts of user interface elements will appear outside screen boundaries.
Watch the video below and use the guide linked below:
More Info available at ModMyi.
Also, Ultrasn0w 1.2.2, will now unlock your iPhone 4 or 3GS running the latest iOS 4.3.2 firmware, allowing you to take your device to any 3G GSM carrier. It requires a jailbroken device with 06.15.00 baseband so you'll probably want to use a tethered jailbreak for iOS 4.3.2. Upon downloading and installing the Ultrasn0w 1.2.2 tool from Cydia, you need to reboot your device using the normal "slide to power off" prior to running the unlock.
Head over to Redmondpie for detailed guide.