It is not an option to remove the sim card and use a pay as you go (PAYG) sim card. Opening up the device with make your warranty null and void.
At WatchOvers, we feel strongly that an SOS emergency device should not be on pay as you go sim , as you cannot risk the service not being available when you need it, i.e. in an emergency. In addition we have found pay as you go services are not usually as good as our service. When our sim cards are roaming, they use the best available network for that location, whether it is our mobile provider or not. With Pay as you go sim cards, you are stuck on 1 network.
In addition for Pay as you go and for many other services, the sim cards can be subject to “steering’ by the sim card provider. Steering is the process by which a mobile operator decides which partner their subscribers will use whilst roaming. These choices are usually exercised to take advantage of better prices from partners or based on bi-lateral agreements they with partners in that location. The quality of better priced networks is not usually as good. As part of our agreement with our mobile provider, our sim cards are not subject to steering.