Disabling a phone (by the manufacturer or by the network provider) can be achieved by two methods primarily:
1. Remove / disable services from the SIM card
2. Remove / disable services from the device using the IMEI number
In scenarion 1, inserting a new SIM card MAY get the phone working again, in scenario 2 a new SIM with not re-enable the device.
Contrary to urban myth, removing the SIM card or powering the device off before the manufacturer/ network operator takes action to deny access to services will not prevent either 1 or 2 working.
I just had an interesting interaction with AIB's servers in relation to my debit card.
I initiated two transaction with the same merchant using the same card within a few minutes of each other today. This seems to have been recognised as "unusual activity" and I got a txt asking me to transmit "Y" to authorise the transaction or "N" to cancel it. Card details were exchanged with the merchant over the phone. AIB Named the merchant, the amount, date & time, last 4 digits of card in the initial txt. I sent "Y" as a message response and got back confirmation of the transaction with the merchant and a message saying it was OK to continue using the card.
My first time experiencing this. I reckon it was a good spot and a nice simple, sensible and secure way to handle it. This is one of the reasons you need a mobile phone for a card account. I know ApplePay and loyalty card use are the other reasons, getting rid of plastic card entirely.