If your phone number shows as unknown on the BlackBerry, you need to contact your carrier as it is SIM related. Depending on the type of SIM card and the carrier, a SIM can hold 2 phone numbers. The BlackBerry can only pull the phone number that is the primary phone number. If you have voice services on the SIM and it shows as unknown, your phone number is probably in the secondary position and hence the handheld can't display it.
As far as I know, carriers can't move a # from secondary to primary on the same SIM card so you will probably have to get a new SIM.