Mobile phone providers commonly lock their phones so they can only be used on their own networks, and not on those of competing carriers. To use ZIP SIM you'll need an unlocked phone.
Here are some tips on how to unlock your phone:
Find an unlocking service
For most phones you can use an unlocking service to get your phone unlocked within 24 hours or less. Just send them your device IMEI (a unique barcode) and they will send you back the unlock code with instructions.
If you prefer to have your phone unlocked in person, visit a local cell phone repair shop. Many offer unlocking services for most phones, but it’s always a good idea to call ahead to make sure they can unlock your specific make and model.
Go to your current provider
After a period of time, your mobile provider may agree to unlock your phone for a small fee.