Hi Jan,
Have you checked the PIN number as outlined above in Waverly's post? If the iPack is configured with a SIM PIN when the SIM doesn't require one, it can cause errors.
In many international applications, SIM cards are setup with PINs. Often times the PIN is '1111' by default. If the SIM card that you use for your personal account is setup this way, and the iPack's SIM is setup this way, you will see the iPack's SIM work in your phone without having to make any security settings changes in your phone.
Cheers,
Dave