MafiaMate is an application to share your Mafia Wars friend codes, so you get a large mob. You can also submit your own code, so others can get you in their mob too.
Install, tap the icon and enter your code. Internet is required. (the codes are pulled from a central database)
Make sure you're connected to the internet, and run the app ;)
New in v2.0:
Now 8 (!) mafia games are supported, instead of one (mafia wars)
Completely free now! No paid version anymore.