ipswDownloader is a very useful application that allows iDevices owners to download any version of iOS directly to their computer without much effort. The application developed by a Ukrainian is currently only available for Mac OS X, but I assume that in the near future there will be a version for Windows users as well. Basically, you download the application, select the model of your terminal, select the iOS version you want and the application will start downloading the firmware to your computer.
The application records the baseband version that the firmware you are going to download installs, displays the program with which you can jailbreak, tells you whether or not you can decode that baseband and how much the respective ipsw occupies. I don't have a Mac handy to test the application, but it seems interesting and very useful.
You can download ipswDownloader from here.
