What are the roaming charge implications for UK or US SIM cards when using CoreESIM in Portugal?

The applicability of 'Roam Like at Home' in Portugal is contingent on your SIM's origin and carrier policy. For EU-issued SIMs, this principle generally applies. However, for UK and US carriers, the situation differs significantly. Post-Brexit, most major UK carriers, such as EE, Vodafone UK, and Three UK, have reinstated daily roaming charges, typically ranging from £2 to £7. US carriers like AT&T, Verizon, and T-Mobile generally offer international day passes at $10-$15 or charge per MB, making a CoreESIM plan a more cost-effective and predictable option for data in Portugal.