20 Most Recent Blackberry 9720 Smartphone - Wireless LAN - 3G - Bar - Black SIM - OS 7.1 Tavor806 MHz - 512 MB - 7.1 cm 2.8" - LCD 480 x 360 - Touchscreen - 5 Megapixel - CameraQuad Band GPS Reciever - Bluetooth - USB - 7 Hour Talk Time - Page 4 Questions & Answers

Backup everything before you doing this. > Plug your device into Blackberry desktop software without your battery in the unit > Click "upgrade" and then let it download the OS > Pop in the battery close to the end of the download and let it do its thing.

yes you have to scan your network or contact your sim service provider to confirm that your sim is working good

It is a junk phone.

https://www.youtube.com/watch?v=wrPLV0n1ttk

you have to go to setting and scroll down and you can see like backup or restore you just enter in and then you can see the option of restore factory

Time for a new phone.

You must call Customer Care for the PUK code. Entering the wrong code can permanently damage your SIM card. 1. Contact Customer Care to request your PUK code. 2. Enter the PUK. 3. Select OK. 4. Enter a PIN of your choice. 5. Select OK. 5. When the 'Confirm New PIN' message displays, re-enter the PIN code. 6. Select OK. The Customer Care Number +1(800)243-0051 (Toll Free)

Device is dead. Need to replace the motherboard

No. Whatsapp is still very much functional on the device.