Another person said:
Short answer: If you like to travel, don't use a Mobile Virtual Network Operator (MVNO).
MVNOs in Ireland are 48, GoMo, Tesco, Clear Mobile, An Post, etc,. You're much better off with the main operators, although 3 should be avoided due to awful customer relations issues.
MVNOs have A LOT of problems providing services when roaming. Over the years, myself and the family have tried a variety of handsets, and have been with 48, Tesco, and GoMo. We always have problems roaming, with no mobile network access at all or only partiel functions (e.g. receive calls but not make them). We have engaged with the support communities and network chat many many times, followed all the best practice and recommended settings, to the point that we now know that MVNOs cannot provide reliable roaming services.
