One thing that has come up numerous times for me while jailbreaking iDevices is to make sure the device can be jailbroken and unlocked. There is a simple little application from iH8sn0w called f0recast that I recommend running before you attempt to jailbreak your iPhone. Use the information below to download and run f0recast on Windows 7.
First visit this link to download f0recast for Windows. The current version is f0recast version 1.2 and the file you download will be named f0recast-V1.2.zip.
Unpack the ZIP file on your Windows computer to reveal the f0recast.exe file.
Run f0recast On Windows:
Now run the f0recast.exe file by double clicking it. It will look similar to the below image before you plug your iPhone into a USB port on your computer.
Plug iPhone Into USB Port On Computer:
Now plug your iPhone into a USB port on your computer to reveal what is possible in terms of jailbreaking and unlocking your iPhone as shown in the below example image.
As you can see above the application is simple but very useful. The f0recast application will provide serial number, baseband version, bootloader version, model number, and what is possible in terms of jailbreaking, tethering, and unlocking the iDevice. Thanks to iH8sn0w.com for providing this useful application!