SOLVED: This method was tested on a Nokia Lumia 720 but should work on ALL Lumias and possibly other Windows 8.0 Smart phones.
Basically I needed the last 8 digits of my sim card number to register to manage my mobile online. Unfortunately I had cut my sim due to a phone change and the numbers did not show. I had also lost the original sim card holder that contained the number. Therefore I was at a loss and needed another way of retrieving my simcard number.
After a bit of playing with my phone I found out how to find it via the Nokia Lumia, here follows the step by step guide.
1. Enter the SETTINGS menu
2. Select ABOUT Windows Phone
3. Click on MORE INFORMATION
4. Look for SIM ID and disregard letter at the end. The rest is your SIM number. I’m pretty sure the number and colon at the start should not be included either. However, if like me you just need the last eight digits of your SIM then just use the last 8 before the letter at the end.