I cannot make or receive calls in my iphone

Are you trying to downgrade or restore your iPhone or iTouch from the official 3.1, 3.1.2 or 3.1.3 Firmware to a Custom Firmware and your iTunes displaying the following 1601, 1602, 16xx or 21 error codes? iH8sn0w has just released a utility named iREB (iTunes Restore Error Bypasser), which provides a workaround to fix these errors.
iREB is available for both Windows and MAC Operating systems. Tool runs on both iPhone & iPhone 3G with Firmware 3.1, 3.1.2, 3.1.3, and also on iPod touch 1G and 2G.
So here is the work around for 1601, 1602, 1604, 16xx or 1621 Error Codes…
New version of iREB is out for 3.1.2 Devices… If you’re upgraded to the latest firmware (3.1.2 or 3.1.3) you should use this download / tool for the errors you’re experiencing. New version has additional devices and more options available.
1. Download iH8sn0w’s iREB 3.1.2 archive for Windows or Mac.
2. Start iTunes and put your iPhone in Recovery Mode; to do so, hold Home and Power button in your iPhone simultaneously and release Power button after a while (10 seconds approx). Keep on holding Home button, till you see following error message appearing in iTunes stating.

3. Now close iTunes and start iREB, following interface will open.

4. Now select your plugged in device in iREB 3.1.2 and it will then show the White creen after few seconds. This happens fast so if you didn’t see it don’t worry… You will also hear sounds (maybe) like your iPhone is being plugged in and unplugged from your computer… That’s normal… The ih8sn0w.exe will crash… That’s normal, as long as you get a white screen…
5. NOTE: If you still don’t see the WHITE screen, you should do this… While the device is still plugged in and iREB running, put your device into the DFU mode. PRESS and HOLD both buttons on your iPhone for 12 Seconds and then release the POWER button (Located at the top of your Device) while still holding down the HOME button… Hold down the HOME button for 30 Seconds… (Yes 30 Seconds) until you get the WHITE Screen, the iTunes will come up with a message stating it found an iPhone in Recover Mode… At this point you can let go of the HOME button… you will be asked to restore this iPhone… and the iREB tool will crash
6. Now start iTunes again and select your device (iPhone/iPod) from iTunes DEVICES tab. 7. To restore original settings on your Apple device, press and hold left “OPTION” button on the keyboard (“SHIFT” button for Windows), iTunes will give you option for Upgrade and Restore, click on “Restore” option in the iTunes and then release the “OPTION/SHIFT” button. Select .ipsw file and restore it