As mentioned in below video a Russian hacker has ported on iphone 4 the maps application, along with 3D maps and turn-by-turn. First he shows that this is the iphone 4 and then runs the maps app, in first instance it seems that the app is typical but later it shows in 3D so we can say that currently it is not perfect. If you want to check you can install on your device the preliminary version. This is also a positive point that the app does not require Cydia to be used for app download.
The detailed information can be found on the this website, the site is in russian but you can use google translate to translate the site in your language. Below I have given steps which are understood by translating the site in my language:
1. You need to download file
2. Connect your iDevice through
3. Write these commands in terminal
apt-get install mobilesubstrate
4. You need do download file on your iDevice. You can do it through FTP, or any file manager for iOS.
5. Enter that command in SSH terminal
dpkg -i file path/file name
6. Reboot your iDevice