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A multi-operator SIM card without steering will not take into account any cost aspect.
When initiating a connection, the object will ask the SIM card to scan all available operator networks.
The SIM card will send it the result and the object will connect, according to its own criteria (usually signal quality), to the best available network.
From now on, use a network provider like M2M Sim Card UK that offers cards that are steering-free.