Get a free PAYG SIM from another network, say O2 and try it out.
Welcome to the EE Community.
In addition to @XRaySpeX's great suggestion, you can find out more information in Unlocking your EE mobile phone or device.
Hope this helps.
@donnalivie, if you know anyone on another network, you could always try their SIM card to see if the phone is unlocked.
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