Before travelling, identify the exact country, the line being used and the intended activity. Using a UK SIM on an overseas network is roaming. Calling abroad while physically in the UK is international calling.
What to establish first
Check the current destination rules, any required activation, the available allowance and fair-use limits. Download the relevant provider instructions before departure and know how to disable data roaming if it is not intended.
Keep the distinction clear
A travel data eSIM may not include ordinary calls or messages. In a dual-SIM phone, check which line handles mobile data and which remains available for calls. Do not infer overseas inclusion from an unlimited UK label.
Open your preparation checklist
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