Phone Number Not Shown in Phone Status

[Guest Billy Wiz]

I have a ZTE Blade/Orange San Francisco running Gingerbread 2.3.5 - Swedish Snow RLS7 on the GiffGaff network in the UK.

The phone number is shown as "Unknown" on the Phone Staus page and everytime I turn the phone on Kaspersky Mobile Security sends a message saying a new sim has been put in the phone - this costs money to send and is reducing my credit unecessarily. How can I get the phone number to be recognised so this doesn't happen?

Thanks in advance.